CONCEPT BASED
1. A force F = 20 + 10y acts on a particle in y-direction where F is in newton and y in meter. Work done by this force to move the particle from y = 0 to y = 1 m is
(a) 5 N (b) 25 N
(c) 20 N (d) 30 N
2. A ball is thrown vertically downwards from a height of 20 m with an initial velocity v0. It collides with the ground, losses 50 percent of its energy in collision and rebounds to the same height. The initial velocity v0 is (Take g = 10 m s−2)
(a) 28 m/s (b) 10 m/s
(c) 14 m/s (d) 20 m/s
3. A block of mass 10 kg is moving along x-axis under the action of force F =5N. The work done by the force in moving the block from x =2m to 4m will be __________ J.
(a) 10 J (b) 25 J (c) 30 J (d) 40 J
4. A particle moves from a point (−2 i+5 j) to (4 i+3 k ) when a force of (4 i +3 j ) N is applied. How much work has been done by the force ?
(a) 8 J (b) 11 J (c) 5 J (d) 2 J
(5) Tell which of the following statements are False?
(a) The forces involved during the elastic collision are non-conservative in nature.
(b) K.E. lost in an inelastic collision appears in some other form of energy such as heat, sound etc.
(c) Mechanical energy is not converted into any other form of energy in an elastic collision.
(d) Coefficient of restitution is zero (e = 0) for a perfectly inelastic collision.
(6) Tell which of the following statement is False?
(a) Friction is a conservative force.
(b) Gravity is a conservative force.
(c) No work is done against gravity while moving an object along horizontal.
(d) Kilowatt-hour is the unit of energy.
(7) Tell which one of the following statement is False?
(a) A truck and car having same K.E. cover equal distances before stopping after applying equal retarding force through brakes.
(b) 1 kg m = 9.8 J
(c) 1 J = 108 erg
(d) For an elastic collision, the velocity of separation after collision is always equal to the velocity of approach before collision.
(8) Which of the following statement is False?
(a) A teacher rubbing the blackboard by a duster is doing no work.
(b) A light and a heavy body have equal K.E. of translation. The heavier body has larger momentum.
(c) A bullet is fired from a rifle. If the rifle recoils freely, then the K.E. of the rifle is greater than that of the bullet.
(d) The energy produced when 10 gram of coal is burnt is 9 × 104 J.
(9) Which of the following statement is True?
(a) Both momentum and energy are conserved in an inelastic collision.
(b) Neither momentum nor energy is conserved in an inelastic collision.
(c) Momentum is conserved but not the K.E. in an inelastic collision.
(d) Momentum is not conserved but the K.E. is conserved in an inelastic
(10) Which of the following statement is False?
(a) The principle of conservation of linear momentum can be strictly applied during a collision between two particles provided the time of impact is extremely small.
(b) In an inelastic collision, the linear momentum is conserved but not the kinetic energy.
(c) The collision is said to be elastic if two bodies stick together after collision.
(d) None
11. Which of the following columns is correctly matched?
| Column I | Column II |
| (a) Conservative force | (i) work |
| (b) Non-conservative force | (ii) force of friction |
| (c) Dot product of F and v | (iii) gravity |
| (d) Dot product of F and s | (iv) Power |
12. Match the column I & II
| Column I | Column II |
| (p) Work done is zero | (i) by gravity |
| (q) Work done is positive | (ii) electrostatic force |
| (r) Work done is negative | (iii) against gravity |
| (s) is a conservative force | (iv) by centripetal force |
(a) (p) – (ii) (q) – (iii) (r)-(i) (s)-(iv)
(b) (p) – (vi) (q) – (iii) (r)-(i) (s)-(ii)
(c) (p) – (iv) (q) – (i) (r)-(iii) (s)-(ii)
(d) (p) – (ii) (q) – (iv) (r)-(i) (s)-(iii)
13. Match the column I & II
| Column I | Column II |
| (p) S.I. unit of power | (i) Electron volt (eV) |
| (q) Unit of energy | (ii) 9.8 J |
| (r) 1 horse power | (iii) Watt |
| (s) 1 kgm | (iv) 746 W |
(a) (p) – (iii) (q) – (i) (r)-(iv) (s)-(ii)
(b) (p) – (iv) (q) – (iii) (r)-(i) (s)-(ii)
(c) (p) – (iv) (q) – (iii) (r)-(ii) (s)-(i)
(d) (p) – (ii) (q) – (iv) (r)-(i) (s)-(iii)
14. No work is done if(a) displacement is zero
(b) force is zero
(c) force and displacement are mutually perpendicular
(d) All of these
15. According to work-energy theorem, the work done by the net force on a particle is equal to the change in its(a) kinetic energy
(b) potential energy
(c) linear momentum
(d) angular momentum
16. If a light body and heavy body have same kinetic energy, then which one has greater linear momentum?(a) Lighter body
(b) Heavier body
(c) Both have same momentum
(d) Can’t be predicted
17. The coefficient of restitution e for a perfectly inelastic collision is(a) 1 (b) 0 (c) infinity (d) –1
18. Unit of energy is(a) kwh (b) joule
(c) electron volt (d) All of these
19. A man pushes a wall and fails to displace it, he does(a) negative work
(b) positive but not maximum work
(c) no work at all
(d) maximum positive work
Directions: (a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.
20 Assertion : A work done by friction is always negative.
Reason : If frictional force acts on a body its K.E. may decrease.
D
NCERT LINE BY LINE QUESTIONS
- A force F = 20 N acts on a object and displaces it from rest to speed of 10 m/s in its direction. What is displacement, if mass of object is 2 kg? [NCERT Pg. 119]
(1) 6m (2) 5 m (3) 12 m (4) 10 m
2. Raindrop is falling downwards under influence of gravity and opposing resistive force. Consider a drop of mass 5.00 g falling from height of 500 m and hits ground with speed of 70 m s_1. What is work done by resistive force? [NCERT Pg. 136]
(1) -7.85 J (2) -9.50 J (3) -12.75 J (4) -13.50 J
3. A cyclist comes to skidding stop in 6 m. During this process the force on cycle due to road is 120 N and is opposing the motion. How much work does road do on cycle?
[NCERT Pg. 117]
(1) -720 J (2) -420 J (3) 20 J (4) Zero
4. A shooter fires a bullet of mass 50 g with speed of 200 m s_1 on softwood of thickness 2 cm. If bullet looses 80% of its kinetic energy and emerges out. What is emergent bullet speed? [NCERT Pg. 118]
(1) 89.4 ms–1 (2) 69.5 ms–1 (3) 100 ms –1 (4) 20.0 ms–1
5. A woman pushes a box on railway platform which has rough surface. She applies a force
of 20 N over a distance of 5 m thereafter gets tired and applied force which reduces linearly
to 10 N with distance. The total distance which box has been moved is 10 m. Work done during second displacement is
(1) 175 J (2) 19.5 J (3) 75J (4) 14.65 J
6. A block of mass m = 1 kg is moving on horizontal surface with speed of 4 m s_1 enters a rough patch ranging from x = 0.1 m tox = 1.6 m. The retarding force in this range is inversely proportional to x
F=-1/x (0.1 <x< 1.6 m)
What is final kinetic energy of the body? [NCERT Pg, 120]
(1) 9.2J (2)7.3J (3) 6.84 J (4) 5.23 J
NCERT BASED PRACTICE QUESTIONS