Work Energy Theorem

Q. A man of mass 60 kg runs up a flight of 30 steps in 40 seconds. If each step is 20 cm high, calculate the power of the man.

Q. The net work done on a body is equals to change in kinetic energy of the body.

1. True
2. False

Q. An object of mass 2 kg is at rest at point A. It starts rolling from point A to point B before coming to a stop at point C. The path from A to B is smooth (no friction), but the path from B to C is rough (presence of friction). Choose the correct statement regarding the energy possessed by the object. (Take g = 10 m/s${}^2$)

1. Mechanical energy at point A is > Mechanical energy at point B
2. Mechanical energy at C = 0
3. Kinetic energy at point B = 30 J
4. Mechanical energy at point B = Mechanical energy at point C

Q. Certain force acting on a 20 kg mass changes its velocity from
5 m/s to 2 m/s. Calculate the work done by the force.

Q. Calculate the work required to be done to stop a car of $1500kg$ moving at a velocity of $72kmph$?

Q.

The kinetic energy of a body changes from 12 J to 60 J due to the action of a force of 5N on an object of mass 4 kg. The work done by the force is:

1. 36 J

2. 24 J

3. 60 J

4. 48 J

Q.

A force of magnitude 35 N acting on a body of mass 4 kg increases its kinetic energy from 0 J to 210 J. The displacement of the body during this interval is___.

1. 4m

2. 3 m

3. 6 m

4. 5 m

Q.

A body of mass 44 kg is moving at a velocity of 10 m/s is brought to rest in 10mins, the work done is:

1. 220 J

2. -2200J

3. 22000 J

4. 22 J

Q. Question 28
Compare the power at which each of the following is moving upwards against the force of gravity?
(i) A butterfly of mass 1.0 g that flies upward at a rate of $0.5m{s}^{-1}$
(ii) A 250 g squirrel climbing up on a tree at a rate of $0.5m{s}^{-1}$

Q. Question 17
The velocity of a body moving in a straight line is increased by applying a constant force F. for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.

Q. A ball is dropped from the top of a tower of an unknown height. If the ball travels 35 m in the last second of its journey, find the height of the tower. (Take g = 10 $m/s^2$)

1. 80 m
2. 60 m
3. 90 m
4. 120 m

Q. From what height should an object be dropped on the Moon so that it's final velocity upon reaching the surface is the same as when droppped from a height of 20 m on the Earth?
Take 'g' on Earth = 10 ms${}^{-2}$.

1. 180 m
2. 60 m
3. 80 m
4. 120 m

Q.

What is the SI unit of energy? Define it.Calculate the kinetic energy of a body of mass 2 kg moving with a velocity of 0.1 metre per second.
[5 MARKS]

Q. Assume the force of gravity to be constant for short heights above the surface of the Earth. A body is dropped from rest at a height h. If we ignore air resistance, what will its kinetic energy be just before it hits the ground?

1. $\sqrt{2h}$
2. $\sqrt{gh}$
3. $\sqrt{2gh}$
4. $\sqrt{4gh}$

Q. An object of mass 2 kg is at rest at point A. It starts rolling from point A to point B before coming to a stop at point C. The path from A to B is smooth (no friction), but the path from B to C is rough (presence of friction). Choose the correct statement regarding the energy possessed by the object. (Take g = 10 m/s${}^2$)

1. Mechanical energy at point A is > Mechanical energy at point B
2. Mechanical energy at C = 0
3. Kinetic energy at point B = 30 J
4. Mechanical energy at point B = Mechanical energy at point C

Q. Calculate the work required to be done to stop a car of $1500kg$ moving at a velocity of $72kmph$?

Q.

A child is moving on a skateboard at the speed of $2\frac{m}{s}$. After a force acts on him, his speed becomes $3\frac{m}{s}$. Find the work done by the external force on the child, given the weight of the child, is 20 kg.

1. 50 J
2. 20 J

3. 100 J

4. 320 J

Q. From what height should an object be dropped on the Moon so that it's final velocity upon reaching the surface is the same as when droppped from a height of 20 m on the Earth?
Take 'g' on Earth = 10 ms${}^{-2}$.

1. 60 m
2. 80 m
3. 120 m
4. 180 m

Q. Question 28
Compare the power at which each of the following is moving upwards against the force of gravity?
(i) A butterfly of mass 1.0 g that flies upward at a rate of $0.5m{s}^{-1}$
(ii) A 250 g squirrel climbing up on a tree at a rate of $0.5m{s}^{-1}$

Q.

A force of magnitude 25 N acting on a body of mass 2 kg increases its kinetic energy from 100 J to 200 J. The displacement of the body during this interval is

___ m.

Q. Calculate the work required to be done to stop a car of $1500kg$ moving at a velocity of $72kmph$?

Q. A loaded bus (mass $m_1$) and an unloaded bus (mass $m_2$) are moving with the same kinetic energy. Brakes are applied to both the buses so as to exert equal retarding force. If $S_1$ and $S_2$ are the distances covered by the two buses respectively before coming to rest, then the ratio ($S_1$/$S_2$) is

1. $\sqrt{\frac{m_1}{m_2}}$
2. ${\left(\frac{m_1}{m_2}\right)}^2$
3. $\frac{m_1}{m_2}$
4. 1

Q.

A force of magnitude 35 N acting on a body of mass 4 kg increases its kinetic energy from 0 J to 210 J. The displacement of the body during this interval is___.

1. 4m

2. 6 m

3. 3 m

4. 5 m

Q. A body of mass m moving with velocity v suffers head on elastic collision with another body of mass 2m at rest. The ratio of the kinetic energy of the colliding body before and after collision is:

1. 16:1
2. 9:1
3. 12:1
4. 18:1

Q.

A bullet of mass 15 g has a speed of 400 m/s. What is its kinetic energy ? If the bullet strikes a thick target and is bought to rest in 2 cm, calculate the average net force acting on the bullet. What happens to the kinetic energy originally in the bullet ?

Q. Compare the power at which each of the following is moving upwards against the force of gravity?
(i) A butterfly of mass 1.0 g that flies upward at a rate of $0.5m{s}^{-1}$
(ii) A 250 g squirrel climbing up on a tree at a rate of $0.5m{s}^{-1}$

Q.

Consider the concepts of work and energy (presuming you have already studied it) and those of impuse and momentum. Force and time is related to momentum change; in the same manner force and displacement pertains to ___________.

1. impulse

2. power

3. energy change

4. velocity

Q.

A force of magnitude 25 N acting on a body of mass 2 kg increases its kinetic energy from 100 J to 200 J. The displacement of the body during this interval is

___m.

Q. Two balls weighing 3 kg and 5 kg are raised to the same height from the ground. Work done on both the balls will be same.

1. False
2. True

Q.

A 50 g bullet moving with velocity 10 m/s strikes a block of mass 950 g at rest and gets embedded in it. The loss in kinetic energy will be