The mass the loaded cart and the height the seat top meters


•	INTRODUCTION

m	m	F
(A)d		F

A teacher applies a force to a wall and becomes exhausted.

The Joule is the unit of work ; 1 Joule = 1 Newton × 1 meter ; 1J = 1 N × m Erg is C.G.S unit and 1J = 107 erg

W = 13.5 J(the angle between F and d is 0° because the F and d are in the same direction).

h m g

m g

m	d
mg	d

So, θ = 90°

W = mgd cos90°

The capacity of an object to do work is called the energy of the object.

The capacity to do work can come through a number of ways. One important way to acquire this capacity is through motion. When a body is moving, it has more energy than when it is at rest. Another way for an object to acquired energy is to be at special positions or in special shapes. There are several other ways of acquiring energy. Let us take at look at some of these.

(ii)	W = mgh hence PE = –mgh

We know that	KE	1 =2mv

K.E	=			p	
K.E	=			m	
K.E	=		p
K.E	=		m +
K.E	p2 =2m

W = ma.d.

and we know that, v2 = u2 + 2 ad

Total work = change in K.E.

i.e. energy neither be created and nor destryod, in absence of external force it change one form to another form

(Isolated system → Net external force acting on it zero)

Hence

–(u2 – u1) = k2 – k1

Illustrations –5: Gravitational potential energy depends upon height (PE = m × g × h). The PE is a minimum when the height is a minimum. Position B is the lowest position in

Power

Force displacement

Power

Work

time

Another common unit of power is horsepower. Horsepower is related to watt as

Power	=	Force	×

❖❖❖❖

➢ ➢	AAccccoorrddiinngg to the work energy theorem, the work done is equal to the change in kinetic energy. The ttoottaall energy (including mass energy) of the universe remains constant.
	Power
	Power = force . velocity

4.

(c) Both (a) and (b) quantities (d) Neither scalar and nor vector

(a) force and velocity
(c) force and momentum

(b) force and mass
(d) force and displacement

The speed of a motor car becomes six times, then the kinetic energy becomes
(a) 6 times	(b) 36 times
	(d) 24 times

		(b) Both K.E. and P.E
	(d) Zero energy
Watt represent the unit for
(a) Energy	(b) Power
(c) Force	(d) Heat

(a) Energy	(b) Power
	(d) Momentum

	(b) kg-ms–1
(c) kg-ms–2	(d) N m-s

*12. A man lift 20 boxes each of mass 15 kg to the height of 1.5 m. The work done by the mass against the gravity is (g = 10 m/s2)
(a) 4500 J (b) 450J
(c) 4.500 J (d) 4000J
13. If a stone of mass 3 kg be thrown with a kinetic energy of 37.5 J. The velocity of stone is (a) 10 m/s (b) 5 m/s
(c) 15 m/s (d) 20 m/s
*14. An object of mass 10 kg is at a certain height above the ground. At what height potential energy of object will be 490 J (g = 9.8 m/s2)

15. 20.	(a) 6 m	(b) 3m
		(d) 7 m

		(b) 56.5 J
		(d) 56 J
	A mass of 10 kg is released from a height 40 m above the surface of the earth. If object at height at 20 m from the surface of earth. The total mechanical energy of body will be
	(a) 2000 J	(b) 4000 J
		(d) 3100 J

		(b) 150 watt
		(d) 200 watt
	If 20000 J of work is done in pumping water up to height 12 m. The amount of water pumped is (g = 9.8 m/s2)
	(a) 170 kg	(b) 150 kg
		(d) 250 kg

		(b) 1.56 × 105J
		(d) 2.5 × 105J
	If a force F is applied on a body and it moves with velocity v1 the power will be
	(a) FV	(b) F/V
		(d) F/V2

A man of mass 60 kg climbs up a 20 m long staircase to the top of a building 10 m high. What is the work done by him ? (Take g = 10 ms2).
(A)	12 kJ	(B) 6 kJ
(C)		(D) 18 kJ

		(B) +490 Joules
(C)		(D) +980 Joules
Which of the following is a scalar quantity
(A) Displacement		(B) Electric field
(C)		(D) Work

(A)		(B)
(C)	6 J	(D) 75 J
A force of 5 N. making an angle θ with the horizontal acting on an object displaces it by 0.4 m along the horizontal direction. If the object gains kinetic energy of 1 J, the horizontal component of the force is
(A)		(B) 2.5 J
(C)		(D) 4.5 J

(A)		(B) 98 J
(C)	3.5 J	(D) none of these
The energy which on e– acquires when accelerated through a potential difference of 1 volt is called
(A)		(B) 1 Electron volt
(C)		(D) 1 watt

*10.A force of 50 N acts on the block at the angle shown in the diagram. The block moves a horizontal distance of 3.0 m. Then the work done by this force

(A) 130.5 J		(B) 129.9 J
		(D) 128.75 J

		(B) 1 × 105 J
		(D) 3 × 105 J
A body of mass 10 kg at rest is acted upon simultaneously by two force 4 N and 3 N at right angles to each other. The kinetic energy of the body at the end of 10 sec is
(A)	100 J	(B) 300 J
(C)		(D) 125 J

(A)		(B) 5 m
(C)		(D) 10m
A body of mass 2 kg is thrown up vertically with K.E. of 490 joules. If the acceleration due to gravity is 9.8 m/s2, then the height at which at K.E. of the body becomes half is original value is given by
(A)	50 m	(B) 12.5 m
(C)		(D) 10 m

Multiple Correct Answer Type
This section contains multiple choice questions. Each question has 4 choices (A), (B), (C), (D), out of which ONE or MORE is correct. Choose the correct options.

16. Choose the correct statement from the following
(A) Kinetic energy of a body is quadrupled, when its velocity is doubled
(B) Kinetic energy is proportional to square of velocity
(C) Kinetic energy does not depend on mass of the body
(D) The change in kinetic energy of a particle is equal to the work done on it by the net force.

18. A man is climbing a staircase. The energy he uses depends on :

(A) the height of the staircase. (C) the time taken to reach the top


		(B) 3000 J
	(C) 3500 J	(D) 3 × 1010ergs

*20. In which of the following work is being done?

	The power supplied by first crane is :	(B) 9800 W
		(B) 9800 W

	The power supplied by second crane is:
	(A) 4900 W

This section contains Matrix-Match Type questions. Each question contains statements given in two

columns which have to be matched. Statements (A, B, C, D) in Column–I have to be matched with

Integer Answer Type

angle between the force and displacement is ( 15 40

. Find the value of n.

	AASSSSIIG GNNM MEENNTT––II
5. 6.	(A) (B) (A) (A) (D) (B) (B) (B) (A) (B)	11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

	(A)			J	KE	2
	a =3m/s 1 2 s = ut + 1 2at 2				KE	2
					= ×2 10 J (A) (D) (A) (C) (A),(B),(C) (A),(B),(C),(D) (A),(C),(D) (B),(D) (A),(C),(D) (A) (B) (A) (A – r, s), (B – q, s), (C – s), (D – p) 8 4 3 7 2 5
		=	5
5. 10. 11.			6
5. 10. 11.	❖❖❖❖