What an object at rest stays at rest and an object in motion with the same speed and in the same direction unless acted upon by an unbalanced force is newton's 1st law of motion?
True
Or
False

The unit for momentum is [tex]kg ms^{-1}[/tex]

Explanation:

The momentum of an object is defined as the product between the mass of the object and its velocity:

[tex]p=mv[/tex]

where

m is the mass of the object

v is its velocity

Let's determine the units for the momentum starting from the mass and the velocity:

Therefore, the unit for momentum is

[tex][p] = [m][v] = (kg)(ms^{-1}) = kg ms^{-1}[/tex]

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Final answer:

The proper unit for momentum, determined using dimensional analysis, is kilogram meters per second (kg·m/s), which is derived from the product of mass (in kilograms) and velocity (in meters per second).

Explanation:

To determine the proper unit for momentum using dimensional analysis, we first need to understand the physical definition of momentum. Momentum (π) is the product of an object's mass (m) and its velocity (v), thus having the formula π = m × v. According to SI units, mass is measured in kilograms (kg) and velocity in meters per second (m/s).

Performing dimensional analysis, we get:

Mass (m): [M] – SI unit: kg

Velocity (v): [LT−1] – SI Unit: m/s

Therefore, the dimensions of momentum are [M][LT−1] = [MLT−1]. When we multiply the units of mass and velocity, we get the unit of momentum as kilogram meters per second (kg·m/s), which is the proper unit for momentum.

Answer:

Explanation:

B)2) Statosphere

E) 5) Exosphere

A) 1) Troposphere

C)3) Mesosphere

D) 4) Thermosphere

Answer:

[tex]\vec u\ . \ \vec v=-138[/tex]

Explanation:

Dot Product of Vectors

The dot product of two vectors is also known as scalar product. Given the vectors  

[tex]\vec u=4\hat i+6\hat j-5\hat k[/tex]

[tex]\vec v=-10\hat i-8\hat j+10\hat k[/tex]

The dot product is  the sum of the products of each component separately

[tex]\vec u\ . \ \vec v=(4)(-10)+(6)(-8)+(-5)(10)[/tex]

[tex]\vec u\ . \ \vec v=-40-48-50=-138[/tex]

Answer:gravity

Explanation:

As Sonja coasts down the hill on her bike, the gravitational potential energy is converted into kinetic energy, which is the energy that increases her speed as she moves downhill.

When Sonja freewheels down the hill on her bike, the primary energy transfer is the conversion of gravitational potential energy to kinetic energy. At the top of the hill, the bike has a certain amount of potential energy due to its elevated position. As she moves downhill, this potential energy is converted into kinetic energy, which is the energy of motion, allowing the bike to increase in speed.

If we were not to ignore friction and air resistance, these factors would cause some of the kinetic energy to transform into thermal energy, due to the friction between the bike tires and the road as well as the air resistance against the rider and the bike.

However, since the question asks us to ignore these factors, we focus solely on the transformation of gravitational potential energy into kinetic energy as Sonja coasts down the hill.

Answer:

Static friction, F=2.9988 N

Explanation:

Static Friction: It is the friction between two or more solid body that are not moving relative to each other.

              When an external force is applied to a body that is in contact with another body, static friction opposes the applied force upto a certain limit, keeping the body at rest. When the applied force exceeds the certain limit the  body begins to move. At that moment applied force is equal to limiting value of  static friction F.

                It varies linearly with normal force(N)

                       F∝N

                         F=μN   (where μ is constant of proportionality and known as coefficient of static friction)

Now,

Mass, m=1.53 kg

Coefficient of static friction, μ=0.2

Normal force, N=m×g

                        =[tex]1.53\times9.8[/tex]     (g=9.8 m/s²)

                         =14.994 N  

Static friction, F= μN  

                         =[tex]0.2\times14.994[/tex]

                          = 2.9988 N                                      

Answer:

In order to move forward, Letti needs to be creative.

Explanation:

Creative:

A person is said to be creative if that person has ability to think out of the box.  

For example: if a person having a problem and instead of using traditional methods of solving the problem then that person thinks about news ideas then that person is creative,

As in our case, letti can use problem solving technique to find a solution of her problem.  

Creative Problem technique:

It is such a problem solving method in which we use unconventional ways to get the solution of a problem. We analyze the problems with news view points so that we can reach at innovative ideas of solutions.

Answer: creative

Explanation: i just took the test

Answer:

5 km

Explanation:

x = |3 - 8| = 5 km

Answer:  c

Explanation:Use equation for speed: V=S/t

S=50 km  -distance

t=15 min=0.25h  -time

V=?

------------------------

V=S/t

V=50km/0.25h

V=200km/h

Answer: 13.6 N

Explanation:

The equation of motion for the rabbit is:

[tex]\Delta x=V_{ox}t+\frac{1}{2}a_{x}t^{2}[/tex] (1)

Where:

[tex]\Delta x=0.85 m[/tex] is the distance traveled by the rabbit

[tex]V_{ox}=0 m/s[/tex] is the rabbit's initial velocity, assuming it started from rest

[tex]t=0.5 s[/tex] is the time

[tex]a_{x}[/tex] is the acceleration

Isolating [tex]a_{x}[/tex]:

[tex]a_{x}=\frac{2 \Delta x}{t^{2}}[/tex] (2)

[tex]a_{x}=\frac{2 (0.85 m)}{(0.5)^{2}}[/tex] (3)

[tex]a_{x}=6.8 m/s^{2}[/tex] (4)

On the other hand, the force [tex]F_{x}[/tex] is given by:

[tex]F_{x}=m.a_{x}[/tex] (5)

Where [tex]m=2 kg[/tex] is the mass of the rabbit

Substituting (4) in (5):

[tex]F_{x}=(2 kg)(6.8 m/s^{2})[/tex] (6)

Finally:

[tex]F_{x}=13.6 N[/tex]

Answer:

The hang time is 2.04 seconds

Explanation:

2-D Motion

It referred to as a situation where an object is launched in such a way it describes a curve, reaches a top height and then returns to ground level after traveling a certain distance x away from the launch point.

Let [tex]v_o[/tex] be the launching speed forming an angle [tex]\theta[/tex] with the horizontal reference. The hang time (time the object remains in the air) is given by

[tex]\displaystyle t_h=\frac{2V_{oy}}{g}[/tex]

Since

[tex]\displaystyle v_{oy}=v_o\ sin\theta[/tex]

Then

[tex]\displaystyle t_h=\frac{2v_o\ sin\theta }{g}[/tex]

We'll use the given values

[tex]\displaystyle v_o=20\ m/s\ ,\ \theta =30^o[/tex]

[tex]\displaystyle t_h=\frac{2(20)sin30^o}{9,8}[/tex]

[tex]\displaystyle t_h=2.04\ sec[/tex]

The hang time is 2.04 seconds

Answer:

A

Explanation:

Pneumonia

c. II and III only (the object has 0 acceleration and the object has  constant velocity.)

Why?

Let's discard each of the given options to find the correct one(s).

False, if an object has a constant speed, it does not mean that there are no forces acting on it, in fact, there will be always acting forces, like frictional force, gravity force, air resistance, and others.

True, in an object is moving at constant speed, it means that there is no acceleration, the speed will be the same all the time during motion.

True, if an object is moving in a straight line at constant speed the velocity will be also constant. The velocity of an object is referring to its speed and its direction, if the object is moving in a straight line, the direction will be the same, so, if the speed is constant, the velocity will be also constant.

Have a nice day!

Answer:

the frequency of this light is [tex]1.5\,\,10^{16}[/tex] Hz (which coincides with the fourth option listed among possible answers)

Explanation:

Recall the relationship between wavelength and frequency of radiation based upon the speed of light in vacuum:

[tex]frequency\,*\,wavelength\,=\, speed\,\,of\,light\\frequency\,*\,wavelength\,=\,3\,\,10^8\,\frac{m}{s} \\frequency\,*\,20 \,\,10^{-9}\,m\,=\,3\,\,10^8\,\frac{m}{s}\\frequency\, =\,\frac{3\,\,10^8}{2\,\,10^{-9}} \,\frac{1}{s} \\frequency\,=1.5\,\,10^{16}\,\,Hz[/tex]

In the process shown above, we have written the speed of light in meters per second, and also converted the 20 nano-meters into meters, in order to reduce SI units properly and have the result shown in units of 1/second (that is hertz's - abbreviate "Hz")

Answer:

[tex]\displaystyle v_2'=7.5\ m/s[/tex]

Explanation:

Conservation Of Linear Momentum

The total momentum of both balls won't change regardless of their interaction while no external forces are acting on the system. We'll use the following variables m1,m2,v1,v2,v1',v2' for the mass of the white ball, the mass of the red ball, their velocities before the collision, and their velocities after the collision, respectively .

The provided data is as follows:

[tex]\displaystyle m_1=143\ gr=0.143\ kg[/tex]

[tex]\displaystyle v_1=7.9\ m/s[/tex]

[tex]\displaystyle m_2=150\ gr=0.15\ kg[/tex]

[tex]\displaystyle v_2=0[/tex]

[tex]\displaystyle v_1'=0[/tex]

To preserve the total linear momentum, the following equation must stand

[tex]\displaystyle m_1\ v_1+m_2\ v_2=m_1\ v_1'+m_2\ v_2'[/tex]

Solving for [tex]v_2'[/tex]

[tex]\displaystyle v_2'=\frac{m_1\ v_1+m_2\ v_2-m_1\ v_1'}{m_2}[/tex]

[tex]\displaystyle v_2'=\frac{0.143(7.9)+0-0}{0.15}[/tex]

The final speed of the red ball is

[tex]\boxed{\displaystyle v_2'=7.5\ m/s}[/tex]

Final answer:

The final velocity of the red ball after the collision, calculated using conservation of momentum, is approximately 1.13 m/s to two significant figures.

Explanation:

Using the principles of conservation of momentum, we can solve for the final velocity of the red ball after the collision. The formula for conservation of linear momentum in a two-object system is m1v1 + m2v2 = m1v1' + m2v2', where m represents mass, v represents initial velocity, and v' represents final velocity. Since the white ball (m1 = 143 g) stops after the collision, its final velocity is 0 m/s. The red ball (m2 = 150 g) is initially stationary, so v2 = 0 m/s. From the data given, we can set up the equation as follows:

143 g × 7.9 m/s + 150 g × 0 m/s = 143 g × 0 m/s + 150 g × v2'

Solving for v2' (the final velocity of the red ball), we get v2' = (143 g × 7.9 m/s) / 150 g. Converting grams to kilograms to use SI units, we calculate:

v2' = (0.143 kg × 7.9 m/s) / 0.150 kg

v2' = 1.13 m/s.

The velocity of the red ball after the collision is approximately 1.13 m/s to two significant figures.

Answer: A:The reproductive system produces hormones.

B:The reproductive system transports reproductive cells.

C:The reproductive system produces reproductive cells.

Explanation:

A:The reproductive system produces hormones. : The reproductive organs ovaries in females and testes in males produces hormones. The ovaries produce estrogen and progesterone and testes produce testosterone.

B:The reproductive system transports reproductive cells. : The ovaries in females transfers an egg into the fallopian tube and testes in males secrete sperms at the time of copulation the fertilization of egg and sperm leads to the development of zygote the precursor of new life.

C:The reproductive system produces reproductive cells.: The ovaries undergo oogenesis and in testes spermatogenesis takes place to develop egg and sperms respectively.

The statements describing the reproductive system are production of hormones and gamete along with the transport. Thus, statements A, B and C are correct.

The reproductive system has been the organ system in the human body that has been function for the reproduction of the organism.

The reproductive system in males has been comprised of testes that produces the male hormones' testosterone. The female reproductive system has been comprised of the ovaries that has been producing estrogen and progesterone.

The male and female reproductive system are responsible for producing male and female gamete and transport them for reproduction.

Thus, the statements describing the reproductive system are production of hormones and gamete along with the transport. Thus, statements A, B and C are correct.

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Answer:

The horizontal component of the velocity is always constant in accordance with the Newton's first law of motion since there is no other force acting in the horizontal direction.

Explanation:

The answers are:

39:

a - 1 mile

b - 0 miles

40:

[tex]a=-4\frac{m}{s^{2} }[/tex]

41:

[tex]Displacement=3.60 miles\\Distance=5 miles[/tex]

Why?

Solving 39:

To answer the questions, we need to remember that distance and displacement are different things. Distance refers to the total "ground" covered during motion, while displacement refers to how far is the object/body from its starting point.

So,

39:

a - the total distance traveled corresponds to the length of the track which is 1 mile.

b - The displacement is equal to 0 because they finished at the starting point,  the distance between the starting and the finishing point is equal to 0.

40:

We can solve the problem using one of the given equations:

[tex]a=\frac{v_f-v_i}{t}[/tex]

Since we know all the information, we just need to substitute it into the equation:

[tex]a=\frac{v_f-v_i}{t}\\\\a=\frac{2\frac{m}{s} -16\frac{m}{s} }{3.5s}=\frac{-14\frac{m}{s} }{3.5s}\\\\a=-4\frac{m}{s^{2} }[/tex]

So, the car's acceleration was -4m/s2 (the car was reducing its speed)

41:

We can solve the problem using one of the given equations (Pythagorean Theorem):

[tex]c^{2}=a^{2}+b^{2}[/tex]

[tex]Displacement=\sqrt{(3mi(North))^{2}+(2miles(East))^{2}}\\\\Displacement=\sqrt{9+4}=\sqrt{13mi^{2}}=3.60miles[/tex]

The distance will be:

[tex]Distance=3mi+2mi=5miles[/tex]

Have a nice day!

Answer:

0.4 m/s

Explanation:

From the law of conservation of momentum, the sum of initial momentum equals the sum of final momentum

Momentum, p=mv where m is the mass and v is the velocity

[tex]m_1v_1+m_2v_2=(m_1+m_2)v_c[/tex] where [tex]v_c[/tex] is the common velocity, [tex]v_1[/tex] and [tex]v_2[/tex] are velocities of Amy and Jenny respectively, [tex]m_1[/tex] and [tex]m_2[/tex] are masses of Amy and Jenny respectively.

Taking forward direction as positive, opposite direction is negative hence [tex]v_1[/tex] is 3 m/s while [tex]v_2=-5 m/s[/tex]

[tex]55 kg\times 3 m/s +(40 kg\times -5 m/s)=(55 kg+40 kg)v_c[/tex]

[tex]95 kg v_c=-35 kg.m/s[/tex]

[tex]v_c=\frac {-35}{95}=-0.368421053  m/s\approx -0.4 m/s[/tex]

Therefore, they travel at 0.4 m/s in the direction of Jenny's movement

Answer:

Impulse = 90

Resulting Velocity = 89

Explanation:

Use F * change in time = m * change in velocity.

For the first part of the question, the left side of the equation is the impulse. Plug it in.

60 * (3.0 - 0) = 90.

For the second half. we use all parts of the equation. I'm gonna use vf for the final velocity.

60 * (3.0 - 0) = 10 * (vf - 80). Simplify.

90 = 10vf - 800. Simplify again.

890 = 10vf. Divide to simplify and get the answer.

The resulting velocity is 89.

The impulse supplied by the booster engine is 180 Ns and the resulting velocity of the 10kg rocket is 98 m/s.

The question involves calculating the impulse delivered by the booster engine of a rocket and its resulting velocity. The impulse is obtained through the relationship Impulse = Force × Time. By applying a constant forward force of 60 N for 3.0 seconds, the impulse can be calculated as:

Impulse = 60 N × 3.0 s = 180 Ns (Newton-seconds)

To find the resulting velocity of the rocket, we use the impulse-momentum theorem which states that the impulse applied to an object is equal to the change in momentum of the object. Since the rocket's mass is constant, the change in momentum can also be expressed as the mass of the rocket times the change in velocity (Impulse = Change in momentum = Mass × Change in velocity). Therefore:

Change in velocity = Impulse / Mass

Change in velocity = 180 Ns / 10 kg = 18 m/s

The initial velocity of the rocket is 80 m/s, so the final velocity of the rocket after the impulse will be:

Final velocity = Initial velocity + Change in velocity = 80 m/s + 18 m/s = 98 m/s

Answer:

a) Dark energy is the cause of the acceleration of the universe, while dark matter is the cause of the formation of structures.

e) There is much more dark energy in the universe, by mass.

Explanation:

Dark energy rises as an explanation of the accelerated expansion of the Universe, since it was expected that this slow down since The Big Bang, as a consequence of the gravitational attraction between the different objects (galaxies, planets, etc) but instead, the observations show how it is accelerating.

Dark matter in the other hand was born to explain why stars that were more farther for the supermassive black hole in the center of the Milky way galaxy didn't decrease their rotational velocity as it was expected.

[tex]v = \sqrt{\frac{G M}{r}}[/tex]  

Where v is the rotational velocity, G is the gravitational constant, M is the mass inside the orbital radius, and r is the orbital radius.

If the distance increases the orbital speed decreases (inversely proportional).

Answer:a and e

Explanation:

Answer:

When have passed 3.9[s], since James threw the ball.

Explanation:

First, we analyze the ball thrown by James and we will find the final height and velocity by the time two seconds have passed.

We'll use the kinematics equations to find these two unknowns.

[tex]y=y_{0} +v_{0} *t+\frac{1}{2} *g*t^{2} \\where:\\y= elevation [m]\\y_{0}=initial height [m]\\v_{0}= initial velocity [m/s] =41.67[m/s]\\t = time passed [s]\\g= gravity [m/s^2]=9.81[m/s^2]\\Now replacing:\\y=0+41.67 *(2)-\frac{1}{2} *(9.81)*(2)^{2} \\\\y=63.72[m]\\[/tex]

Note: The sign for the gravity is minus because it is acting against the movement.

Now we can find the velocity after 2 seconds.

[tex]v_{f} =v_{o} +g*t\\replacing:\\v_{f} =41.67-(9.81)*(2)\\\\v_{f}=22.05[m/s][/tex]

Note: The sign for the gravity is minus because it is acting against the movement.

Now we can take these values calculated as initial values, taking into account that two seconds have already passed. In this way, we can find the time, through the equations of kinematics.

[tex]y=y_{o} +v_{o} *t-\frac{1}{2} *g*t^{2} \\y=63.72 +22.05 *t-\frac{1}{2} *(9.81)*t^{2} \\\\y=63.72 +22.05 *t-4.905*t^{2} \\[/tex]

As we can see the equation is based on Time (t).

Now we can establish with the conditions of the ball launched by David a new equation for y (elevation) in function of t, then we match these equations and find time t

[tex]y=y_{o} +v_{o} *t+\frac{1}{2} *g*t^{2} \\where:\\v_{o} =55.56[m/s] = initial velocity\\y_{o} =0[m]\\now replacing\\63.72 +22.05 *t-(4.905)*t^{2} =0 +55.56 *t-(4.905)*t^{2} \\63.72 +22.05 *t =0 +55.56 *t\\63.72 = 33.51*t\\t=1.9[s][/tex]

Then the time when both balls are going to be the same height will be when 2 [s] plus 1.9 [s] have passed after David throws the ball.

Time = 2 + 1.9 = 3.9[s]

Answer:

The static friction is 5 N acting in the direction opposite to that of the force of push.

Explanation:

Given:

A book lying on a table. Force of push is 5N.

Now, the book is not moving. This clearly means that some resistive force is acting in the opposite direction which has the same magnitude as that of the applied force, thus making the net force acting on the book equal to zero.

This resistive force acting in the opposite direction is called the static frictional force.

Therefore, the static friction acting on the book is equal to 5 N and acts in the direction opposite to that of the force of push.

Answer: not having a portable ladder extend 3 feet above the landing

improper use of the top of step ladders

lack of work or training

Explanation: career safe online

The top three OSHA cited ladder violations are improper maintenance, improper use, and missing fall protection systems, endangering worker safety.

These violations are common because they relate to fundamental ladder safety. Maintaining a ladder's condition is crucial to ensure it's safe for use. Inadequate ladder use includes actions that increase the risk of falls, such as reaching too far or using a ladder not designed for the task.

Missing fall protection is a serious violation, especially when working at heights where a fall could lead to severe injuries or fatalities. Employers must ensure proper ladder training, maintenance, and use, and provide the necessary safety equipment to protect workers from fall hazards. Violations in these areas can result in OSHA citations and penalties.

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Answer:

λ = 0.28m

Explanation:

Equation used is v = λf, where v is velocity, λ is wavelength, and f is frequency

We need to find wavelength so rearrange the equation in term of wavelength.

v = λf

λ = f/v

We know that period is the inverse of frequency (f = 1/T), so lets substitute that into our equation

λ = f/v

λ = (1/T)/v

Plug in your the given values given in the question.

We're given v=12m/s and T=3sec

λ = (1/T)/v

λ = (1/3)/12

λ = 1/36 = 0.2777777 = 0.28m

Final answer:

The wavelength of a wave with a 3-second period traveling at 12 m/s is 36 meters.

Explanation:

To find the wavelength of a wave, you can use the formula:
wavelength = wave speed x period. In this case, the period of the wave (T) is 3 seconds and the wave speed (v) is 12 m/s.

wavelength = 12 m/s  x  3 s = 36 meters.

Therefore, the wavelength of the wave is 36 meters.

Answer:

Option C

100 J

Explanation:

Kinetic energy, KE is given by

[tex]KE=0.5mv^{2}[/tex] where m is the mass and v is the velocity

Substituting 50 Kg for mass, m and 2 m/s for velocity v then we obtain

[tex]KE=0.5*50*2^{2}=100 J[/tex]

Therefore, the child's kinetic energy is equivalent to 100 J

Answer:100J

Explanation:

a) The momentum of the third piece is 19.1 kg m/s

b) The velocity is 6.4 m/s at an angle of [tex]-65^{\circ}[/tex]

Explanation:

a)

We can solve this problem by applying the law of conservation of momentum in 2D. In fact, the total momentum of the board before the explosion must be equal to the total momentum of the 3 pieces after the explosion.

Before the explosion, the total momentum is zero, since the board is at rest. Resolving into the x- and y- components, this means that the two components of the momentum are zero:

[tex]p_x = 0\\p_y = 0[/tex]

After the explosion, we have:

[tex]p_x = (2 kg)(10 m/s)( cos 60^{\circ}) + (1.2 kg)(15 m/s)(cos 180^{\circ})+p_{3x}[/tex]

where [tex]p_{3x}[/tex] is the x-component of the momemtum of the 3rd piece. By solving,

[tex]p_x = -8+p_{3x}[/tex]

And since the x-momentum must be conserved,

[tex]0=-8+p_{3x} \rightarrow p_{3x}=8 kg m/s[/tex]

Similarly, along the y-axis,

[tex]p_y = (2 kg)(10 m/s)( sin 60^{\circ}) + (1.2 kg)(15 m/s)(sin 180^{\circ})+p_{3y}[/tex]

where [tex]p_{3y}[/tex] is the y-component of the momemtum of the 3rd piece. By solving,

[tex]p_y = 17.3+p_{3y}[/tex]

And since the y-momentum must be conserved,

[tex]0=17.3+p_{3y} \rightarrow p_{3y}=-17.3 kg m/s[/tex]

So now we can find the momentum of the third piece:

[tex]p_3 = \sqrt{p_{3x}^2+p_{3y}^2}=\sqrt{8^2+(-17.3)^2}=19.1 kg m/s[/tex]

b)

The momentum of the third piece is given by

[tex]p_3 = m v_3[/tex]

where

m = 3 kg is the mass of the piece

[tex]v_3[/tex] is the velocity

Solving for [tex]v_3[/tex], we find

[tex]v_3 = \frac{p_3}{m}=\frac{19.1}{3}=6.4 m/s[/tex]

We can also find the direction, which is identical to the direction of the momentum, by using the following equation:

[tex]\theta = tan^{-1}(\frac{p_{3y}}{p_{3x}})=tan^{-1}(\frac{-17.3}{8})=-65^{\circ}[/tex]

So, the third piece flies off at 6.4 m/s at an angle of [tex]-65^{\circ}[/tex].

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Answer:

0m

Explanation:

In physics this is 0m, why?

Okay so, you moved 60 meters (in position/m) the first 10 seconds (sec) and then between 10 and 15 seconds, you took a brake and didn't move. (The graph is still because the time is constant and your motion is 0 meters).

When 15 seconds have passed, you go back where you were, exactly at 0 meters, your initial position.

In reality would this be 60 meters + 60 meters back which would be 120 meters, or 0.12km if you will. But in physics world, it's 0 meters in position.

Hope you understood!

Good luck!

Astrophysicist Dr. D

Answer:

120 m

Explanation:

The displacement from 0 s to 30 s is 0 m, since the change in position between those points is 0 m.  However, we are asked to find the distance traveled, not the displacement.

The object travels 60 m forward, then 60 m backward.  So the total distance traveled is 120 m.

Answer:

A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator.

Explanation:

Answer:

a) solar activity -- sudden eruptions of large bubbles of plasma and magnetic energy

and

d) solar flare -- sudden release of magnetic energy

Explanation:

We can start by eliminating the options that are definitely wrong.

A coronal mass ejection is not a relatively cool spot on surface of the sun, in fact such a spot is a sunspot, while a coronal mass ejection occurs when the  magnetic field of the sun emerges as a loop. Thus, both options B and E are incorrect, leaving only A,  C, and D. Option C makes no sense, as the sun's gravitational field does not 'churn'. Thus, only options A and D are left. A closer look at A and D reveals they are correct; solar flares are in fact sudden releases of magnetic energy, as seen in this quote from UC Berkeley's website; "Solar flares are caused by sudden changes of strong magnetic fields in the Sun's corona.". And solar activity is a blanket term for the effects of eruptions of plasma and magnetic energy from the sun.