WORK, ENERGY AND POWER

SECTION 1: MULTIPLE-CHOICE QUESTIONS

1. A pendulum bob is released from point P above a horizontal surface. At the
lowest point, Q, of its swing , it collides with a stationary block situated on a
frictionless horizontal surface , as shown below. Ignore air friction .

pendulum
bob block

Q horizontal surface

Which ONE of the following combinations of conservation laws can be used

to calculate the speed of the bob at Q immediately before and after colliding
with the block?

SPEED AT Q SPEED AFTER COLLISION

A Conservation of mechanical energy Conservation of linear momentum
B Conservation of linear momentum Conservation of mechanical energy
C Conservation of mechanical energy Conservation of mechanical energy
D Conservation of linear momentum Conservation of linear momentum (2)

2. A person lifts a crate vertically upwards at constant velocity through a distance

h. The person does work x on the crate in time t.
The person now lifts the same crate vertically upwards at constant velocity
through the same distance, but in time 2t.
The work done by the person on the crate will now be ...
A. ½x B. x
C. 2x D. 4x (2)

3 . A constant horizontal force F displaces a box by bi..x over a rough horizontal

surface. Study the diagram below.
;.-----bi..x-----.,
r-----~
I I
I I
• • surface

The normal force acting on the box does NO work on the box during the
motion, because it is .. .
A . equal to the applied force.
B . perpendicular to the applied force.
C . equal and opposite to the weight of the box.
D . perpendicular to the displacement of the box . (2)
;;tail# -~ ------- ==:"E-1·: :•,seser*'** ifl6A s
 4. The net work required to stop a moving object is equal to the ...
A inertia of the object. .
B hange in kinetic energy of the obJect.
C · \ange in momentum of the object.
D.· ~hange in impulse of the object. (2)

m is released from rest from the top of a frictionless inclined

5 A block of mass
. lane QR, as shown below. . .
P I mechanical energy of the block is Ea at ~omt Q and ER at po,_nt R.
The t~ta . of the block at points Q and R 1s Ka and KR respectively.
The k1net1c energy

L-- - - - - - - - ~ R
Which ONE of the statement regarding the total mechanical energy and the
kinetic energy of the block at point Q and R respectively is CORRECT?
TOTAL MECHANICAL ENERGY E KINETIC ENERGY K
A Ko> KR Ko = KR
8 Ko= KR Ka < KR
C Ko = KR Ka = KR
D Ko < KR Ka > KR (2)

6. Which ONE of the following statements is always TRUE for inelastic collisions
in an isolated system?
A. Both momentum and kinetic energy are conserved .
B. Both momentum and kinetic energy are not conserved.
C. Momentum is conserved, but not kinetic energy.
D. Kinetic energy is conserved, but not momentum. (2)

?. When the net work done on an object is positive (greater than zero), the ...
A. kinetic energy of the object is zero.
B. kinetic energy of the object is increasing.
C. kinetic energy of the object is decreasing.
D. kinetic energy of the object remains unchanged. (2)

8
· Th~ w~rk done by a constant force F applied to an object to increase the
ObJect s speed from v to 2v is w.
T~1e bwork done by the same force to increase the speed of the object from O to v
WI 1 e ...

A. %W B. ½W C . 2W D . 3W (2)
 ,
1
s b e lo w correc tly r ep r ese n ts t h e re l at\onsh\p
0
s . VVhic h O N E k ~te,..,te,·cger~~ rgy (K) o f a fre e- falling object and its speed (v)?
between th e ,n
B.
A

v (m-s-1) v (m-s-1)

C.

--
D.
-,
:::.:::'.

v (m-s-1) v (m-s-1) (2)

10. The graph below represents the relationship between the work done on
an object and the time taken for this work to be done.

Time(s)
The gradient of the graph represents the ...
A . power. B. momentum.
C. kinetic energy. D. potential energy. (2)

11 . The speed of a bicycle increases from 2 m-s- 1 to 8 m-s- 1. Its kinetic

energy increases by a factor of ...
A. 4 B. 6
C. 8 D. 16 (2)

12. Two balls, P and Q , are dropped simultaneously from the same height.
Ball P has TWICE the mass of ball Q . Ignore the effect of air friction .
Just before the ball hit the ground , the kinetic energy of ball Pis x.
The kinetic energy of ball Q, in terms of x, will be .. .
A. {x B. }x
C. x D. 2x (2)
 •;;p;5g iffli*AY e,eD CAWPft M

13. If air resistance is negligible, the total mechanical energy 0 f f .

body . . . a ree-fa\\mg

A. remains constant. B. becomes zero.

C . increases. D. decreases. (2)

14. If the momentum of an object is doubled, then its kinetic energy is .. .

A. halved . B. doubled.
C. three times greater. D. four times greater. (2)

15. Power is defined as the rate ...

A. of change of velocity.
B. at which work is done.
C. of change of momentum.
D. of change of displacement. (2)

16. Which ONE of the following physical quantities is equal to the product of
force and constant velocity?
A. Work B. Power
(2)
C. Energy D. Acceleration

17. The free-body diagram below shows the relative magnitudes and
directions of all the forces acting on an object moving horizontally in
an easterly direction.
normal force

frictional force
....- - - - - - ~ applied force
s
weight

The kinetic energy of the object ...

8. increases.
A. is zero. (2)
D. remains constant.
C. decreases.
18. A car moves up a hill at CONSTANT speed . Which O~E of the followin~?
represents the work done by the weight of the car as 1t moves up the htll . (2)
A . AEk 8. AEp C. -AEk D. -AEp
th
19. An object moves in a straight line on a ROUGH horizontal surface. If e
net work done on the object Is zero, then ...
A. the object has zero kinetic energy.
8. the object moves at constant speed .
C. the object moves at constant acceleration. (2)
D. there is no frictional force acting on the object.
20 . An object is pulled along a straight horizontal road to the right without being
lifted . The force diagram below shows all the forces acting on the object.
F
N

w
Which ONE of the above forces does POSITIVE WORK on the object?
A. w B. N C. f D. F (2)

21 . The kinetic energy of a car moving at constant velocity vis K. The velocity
of the car changes to 2v. What is the new kinetic energy of the car?

B. ~K C. 2K D. 4K (2)

22. The graph below represents a constant force F acting on an object over a
displacement x. The force and displacement are in the same direction.

force (N)

F ....---------

O.___ _ _ _ _ ___.__ displacement (m)

X

Which ONE of the following statements can be deduced from the graph?
A. The gradient of the graph represents the work done by the force .
B. The gradient of the graph represents the change in kinetic energy of
the object.
C. The area under the graph represents the net work done by the force .
D. The area under the graph represents the power dissipated by the force. (2)

23. For a body falling from a GREAT height in the absence of air resistance ,
which ONE of the following statements regarding kinetic energy (Ek) and
gravitational potential energy (Ep) is TRUE at ALL points of the motion?
A. Ep - Ek= constant 8. Ep + Ek= constant
2
C. Ek is equal to Ep D. Ek is less than Ep ( )

24 . A ball is thrown vertically upwards. Which ONE of the following physical .

quantities of the ball will be ZERO when the ball reaches its maximum height?
A. acceleration B. kinetic energy
D. weight (2)
C . gravitational potential energy
 25. In a playground there are two frictionless slides, A and B, with the heights
as indicated in the diagram below. Catherine slides down A and then
down B. 5m

How will Catherine's velocity at the bottom of slide B compare to her

velocity at the bottom of slide A?
Her speed at the bottom of ...
A. A is twice as much as the speed at the bottom of B.
8. B is twice as much as the speed at the bottom of A.
C. B is more, but not twice as much as the speed at the bottom A.
D. Bis equal to the speed at the bottom of A. (2)

26. An object, with mass m, is accelerated vertically upwards by an applied force

F acting on it. (Ignore all effects of friction.)

Which ONE of the following is true for the work done by the applied force F
and the net force Fnet respectively?

WORK DONE BY F WORK DONE BY Fnet

A LiU + LiK ½mv2
B LiU - LiK ½mv2
C LiU + LiK LiK
D mgh + ½mv2 LiK (2)
27. A_ball is dropped from rest, in the absence of air resistance, from a height 3h
with m~chanical energy equal to E. If the ball reaches a height of h,
the kmet,c energy of the ball is equal to .. .
A \E B. ~E C. E D. ~E (2)
2
8. Which action stated below requires NO work to be done on that
specific object?
A. lifting an object from the floor to the ceiling.
B. Moving an object along the floor against friction .
C. Decreasing the speed of an object until it comes to rest.
(2)
D . Holding an ob1ect stationary above the ground.
JiS?li 1 t L a t ,
 111,;j11...-:-.~J!l'.:'a~~-..:.-=-:-•~~~-=------..... I d I 0 ...
• '::witW1r('t:liatSl WOIIIK. ENl'JllOt;AND,tQ ~vmf

29. The diagram below shows a track , ABC . The curved secti on , AB, is
frictionless . The rough horizontal section , BC , is 8 m long .
A

T.m:
4

ll-------------~~~~~~~~~r~-,1/~
B+---8m----C
An object of mass 10 kg is released from point A which is 4 m above the
ground. It slides down the track and comes to rest at point C.
Which ONE of the following statements about the mechanical energy of
the 10 kg mass is INCORRECT?
A. The mechanical energy increases from A to B.
B. The mechanical energy decreases from B to C.
C. The mechanical energy at B is equal to the kinetic energy at B.
D. The mechanical energy is not conserved from B to C, but is
conserved from A to B. (2)

30. A car travels along a straight level road with constant acceleration. Which
ONE of the following power (P) versus velocity (v) graphs best represents
the motion of the car?
A. 8.

p p

V V

C. D.

(2)
V V

31. A book is pushed across a rough surface by force of magnitude F while

experiencing a frictional force of magnitude f. The average constant
speed of the book is v. Which ONE of the following expressions gives the
rate at which the kinetic energy of the book changes?
A. (F + /)v 8. (F - / )v
C. (-F - /)v D. (F x f )v
 3i2.. ~~dtrecr..,.,, d:t,~ ~ irll • ..

A S.. .
- ~ grliN~~~
-- . -~ 0.

33.. Aco;~batisabt;e ___

A. b ~ wott naq a n ~ l's-.,er- 1 -
~ ~d t h e ~ ~ 'lS

a b r ~ e:ewcn~ im an~w~ .
••· t--~ ._ lS '"'d.

C. tor•ftd. ·t ne~cbne mca~ ~ ~ ~ ·h i l o ~ s

~ :dtbe~~
D. 1111.-.b .s equal iR ~~'Ce. o o t ~ in ~ ~a
~bt;e..

34.. Anobjednooes in a stJ~fneon a R O U G H ~ ~

Wthe net Wl'.R done on the object is 2ERO, __ _
A. the objed has ZERO metic enelg)!-
8.. the objed mtWeS at constam speed.
C. lhe objed mcwes with constant acceleration.
o_there is no flidional Jora3 acting on the object.
35.. The graph bekM show the relationsru? beh\-een the a.~~ tFl
on an object and the ~ t (x) of the object in hl ~ "' of !he
applied force_

z
- 1 -------------- '

''
:'
0
lL _____
4x''' __.. displaoon~t(n,)
'
The average wortc in joules~done by the applied force for a dispt~t"'tm ~.r:~
of 4x m is ....
8 . 2x C. 3x 0. 4x
A. ½x

36. A ball is dropped from height h above the ground and th$ gt'QUt"'1
with kinetic energy E. From which height must the ball ba d ~ i to ,-...~
the ground with kinelic energy 2E? (Ignore all effect$ of~\.)
A. 2h B. 3h C. 4h 0. at\ (')

37. An object.moving with a oonst:ant speed v has a kineU~ ~,&f9,Y I . one

of the following will be tru@ for the klnaUo energy tf the object has tl 00t1St1nt
velocity of 2v?
A. ½E B. E C. 2E O. 4E (2)

j S!?55 E ! •!W&MW :Pb i .id iitl! Lil R t33

r
38 . A net fo rce F accelerates two isolated objects , P and Q , from rest on a
straight line for time t as shown below. Object P experiences an acceleration
of a and object Q an acceleration of 2a .
p
F Q
I ) F
If the amount of work done by net force Fon object P equals W , the amount
of work done on Q will be .. .
A. W
B. ½W
C. 2W
D. 4W (2)
39 . A stone is thrown vertically upwards into the air. Which combination in the
table below shows the correct change in the momentum and the potential
energy of the stone? (Ignore the effects of air friction)

Momentum Potential energy

A Increases Decreases
B Decreases Increases
C Increases Increases
D Decreases Stays constant
(2)

40. A ball is thrown vertically upwards. Which ONE of the following physical
quantities of the ball will be ZERO when the ball reaches its maximum height?
A. kinetic energy B. gravitational potential energy
C. acceleration D. weight (2)

41. A stone falls freely from rest from the top of a building. Ignore air resistance.
As the stone falls through the air, which ONE of the following graphs best
represents the relationship between the kinetic energy (K) of the stone
and its displacement (/1y)?
A. B.

K K

b.y b.y

C. D.

K K

~y /j.y (2)
 l
42. (Ep + Ek) top= (Ep + Ek) bottom when only . . . are present.
A frictional forces B. tension forces
c. applied forces D . gravitational forces (2)

_ In the diagram below, two Identical blocks A and B, each with mass m, are
43
placed in the positions as shown below.

fl
2h

i
How does the gravitational potential energy (U) of the blocks compare?
A UA = ½Us B. UA = Us
(2)
C. UA = .J2Us D. UA = 2Us

44. Which ONE of the following equations represents the principle of the
conservation of mechanical energy?
A. 6Ek = 6Ep B. 6Ep = -6.Ek
D. 6-Ep - 6-Ep = Wnc (2)
C. 6Ek + 6Ep - Wnc = 0

45. A car moves from rest in a straight line under the influence of a constant
net force. Which ONE of the following graphs best represents the net work
done (W) on the car in relation to its displacement(ru<)?
A. B.

w w

C. D.

w w

Ax
46. Th e Phys1ca
· t quantity
· energy, expressed in base units. is ...
A. kg -m2-s-3 B. kg -m2-s-2
C. kg -m-s-1 o. kg -m -s-2