Work and Energy Multiple Choice Questions
1. When a body falls freely towards the earth, then its total energy
(a) increases
(b) decreases
(c) remains constant
(d) first increases and then decreases
Ans. (c) remains constant
Explanation: When a body falls freely towards the earth, it obeys the law of conservation of energy. Due to this, its total energy remains constant.
2. A car is accelerated on a levelled road and attains a velocity 4 times of its initial velocity. In this process the potential energy of the car
(a) does not change
(b) becomes twice to that of initial
(c) becomes 4 times that of initial
(d) becomes 16 times that of initial
Ans. (a) does not change
Explanation: Potential energy depends on the height at which the object is situated. In this case, there is no change in height of the object. Hence, there is no change in its potential energy.
3. In case of negative work the angle between the force and displacement is
(a) 00 (b) 450 (c) 900 (d) 1800
Ans. (d) 1800
Explanation: When force and displacement are in mutually opposite direction, the work done is said to be negative. In this case, the angle between the force and displacement is 1800.
4. An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass is 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are 10 m above the ground, they have the same
(a) acceleration
(b) momenta
(c) potential energy
(d) kinetic energy
Ans. (a) acceleration
Explanation: Momentum, potential energy and kinetic energy depend on mass of the object; as well as on some other factors. But acceleration in this case is the acceleration due to gravity; which does not depend on mass or velocity. So, options (a) is correct.
5. A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a levelled road. The work done against the gravitational force will be (g =10 ms–2)
(a) 6 ×103 J
(b) 6 J
(c) 0.6 J
(d) zero
Ans. (d) zero
Explanation: In this case, direction of work done is perpendicular to the direction of gravitational force. Hence, work done against gravitational is zero.
6. Which one of the following is not the unit of energy?
(a) joule
(b) newton metre
(c) kilowatt
(d) kilowatt hour
Ans. (c) kilowatt
7. The work done on an object does not depend upon the
(a) displacement
(b) force applied
(c) angle between force and displacement
(d) initial velocity of the object
Ans. (d) initial velocity of the object
Explanation: Work done is the product of force and displacement. Hence, work done depends on displacement, force applied and on the angle between force and displacement. But it does not depend on initial velocity of the object.
8. Water stored in a dam possesses
(a) no energy
(b) electrical energy
(c) kinetic energy
(d) potential energy
Ans. (d) potential energy
Explanation: The energy stored in an object because of its position is called potential energy. Water stored in dam possesses energy because of its current position.
9. A body is falling from a height h. After it has fallen a height h /2 , it will possess
(a) only potential energy
(b) only kinetic energy
(c) half potential and half kinetic energy
(d) more kinetic and less potential energy
Ans. (c) half potential and half kinetic energy
Explanation: When the body is at height h; its potential energy is at maximum and kinetic energy is zero. When the body hits the ground, its potential energy becomes zero and kinetic energy is at maximum. At mid-way, i.e. half the height; its potential energy becomes half of the maximum and same happens to the kinetic energy.
