For each of the questions, there are four possible

choices. Choose the one you consider conect andrecord your choice.

IVs l. A block of ice is sliding at a constant speed

before moving up a smooth slope as shown.

What are the changes in its kinetic energy and

gravitational potential energy as it is sliding up

the slope?

constant speed-----------)

4. Abox of mass 2 kg is being pushed horizontallyon a smooth surface by a l0 N force for 6 m.

What is the work done on the box by the l0 Nforce?

10N I

----------t 'I2

+---- ----->6m

B 48JD I2OJ

U

\Vg

MCI

kg

A I2JC 6OJ (

lce

5. Abox of mass 2 kg is being pushed horizontally

on a rough surface by a l0 N force for 6 m.

Given that the friction between the box and the

surface is 4 N, what is the work done on the box

by the l0 N force?

+------o-g------>

Kineticenergy

A increase

B increase

C decrease

D decrease

Gravitationalpotential energy

increase

decrease

increase

decrease (

10N 2ke i

t-----r

U A 24tC 6OJ

<-4N

B 36JD IZOJ

d

2. A car is accelerating up a slope. What are the

changes in its kinetic energy and gravitationalpotential energy as it is moving up the slope?

Kinetic Gravitationalenergy potential energy

A increase increase

B increase decrease

C decrease increase

D decrease decrease ( )

3. Abox is being pushed horizontally on a smooth

surface by a l0 N force for 6 m. What is the

work done on the box by the 10 N force?

tON r-----l l--------lzi ll+---- ----->6m

A O.6J B I.1JC I6J D 6OJ

6. Abox of mass 2 kg is being pushed horizontallyon a smooth surface by a l0 N force for 6 m.

What is the work done on the box by the weightofthe box? (g = 10 N kg-')

2ke :

+---- ------)6m

A OJ B I2JC 6OJ D I}OJ )

(

39 Unit 7 Energ, Work and Power

UNIT 7

Energy, Work and PowerMechanics

Theme 2

I*I)

()

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7 . Abox of mass 2 kg is being pushed horizontally

by a l0 N force for 60 cm along the floor.

During the first 20 cm, the friction between the

box and the floor is 4 N, and the friction for the

rest of the distance is negligible. What is the

work done on the box by the l0 N force?

A2J B3J C4I D6J ( )

8. A box of mass 2 kg is moving at a constant

speed of 3 m s-r. What is the kinetic energy ofthe box?

A2J B3J C9J Dl8J( )

9. A box of mass 500 g is moving at a constant

speed of 72 km/h. What is the kinetic energy

of the box?

A 5J B 1OOJ

c r296J D r296000J ( )

10. A box of mass 2 kg increases its speed from3 m s I to 7 m s-r. What is the increase in kineticenergy?

A4I Bl6J C40J D32I ( )

11. A box of mass 2 kg is lifted vertically upwards

by 3 m. Given that the acceleration due togravity is 10 m/s2, what is the gravitationalpotential energy gained by the box?

A0.6J86.71 Cl5J D60J( )

12. A box of mass 2 kg is lifted diagonally frompoint A to point B as shown. Given that the

acceleration due to gravity is 10 m s 2, what is

the gravitational potential energy gained by the

box?

B

d

U

5m,'3

A 2OJ

C 8OJ

4m

B 6OJ

D IOOJ ()

a

U

\Vg

A

13. There are 3 paths leading to the top of the hill as

shown. Assuming that the friction of the ground

is negligible, which of the following statement

is true?

path A(10

Path Bm)

A Path C requires most energy to reach the

top.

B Path B requires the least energy to reach the

top.

C Path B requires more energy than path A toreach the top.

D All three paths require the same amount ofenergy to reach the top. ( )

14. A box of 2 kg mass moves up a ramp frompoint A to point B at a constant speed. Giventhat the surfaces are smooth (frictionless), whatis the gain in the potential energy by the box?(g=10Nkg-')

B

6m

5m m4

3m

A 8OJ

C 2OOJ

B lOOJ

D 22OJ ()

path C(12 m)

m

40 Unit 7 Energy, Work and Power

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15. A pendulum bob pivots at point P, startsswinging from point S. Assuming that there is

no loss ofenergy to the surrounding, at whichposition will the bob next come to a momentary

rest?

P

D

Cs

B

A ()

d

16. Three different stones are being lifted from the

ground level to different heights on differentplanets as given below.

Case 1: A 250 g stone lifted to l0 m on Earth

Case 2: A 6 kg stone lifted to 2 m on the

MoonCase 3: A 1 kg stone lifted to I m on Jupiter

Given that the acceleration due to gravityon Earth, the Moon and Jupiter are l0 m s-2,

2ms-2 and25 m s-2 respectively, which ofthefollowing statements is true?

A More energy is required for case 2 thancase 1.

B More energy is required for case I than

case 3.

C Case 1 and case 2 require the same amount

of energy.

D Case I and case 3 require the same amount

ofenergy. ( )

17. Abox is being pushed horizontally on a smooth

surface by a 10 N force for 6 m. What is the

increase in the kinetic energy of the box?

A O.6J

C I6JB I.7JD 6OJ (

IVg

v

u

V,

18. A 1.2 kg box is being pushed horizontally on a

smooth surface by a l0 N force for 6 m. Giventhat the box is initially at rest, what is the speed

of the box at the end of the 6 m?

A 2ms-rC 50ms-l

B l0ms-'D 100ms-t ()

19. A 6 kg box is being pushed horizontally on asmooth surface by a l0 N force for 6 m. Giventhat the box has an initial speed of 4 m s-r, whatis the speed of the box at the end of the 6 m?

_r5;;;

A 2.0ms'C 6.0ms'

B 4.5ms'D lOmsl ()

20. A6 kg box is being pushed horizontally on asurface by a 10 N force for 6 m. Given that the

box has an initial speed of4 m s-rand the floorhas a limiting friction of 2 N, what is the speed

of the box at the end of the 6 m?

l0N6kg---------n

A 2.0 m s-t

C 5.7 m s-'

B 4.5 m s-'

D l0ms-' ()

1. A 6 kg box is being pushed horizontally on asurface by a l0 N force for 6 m. Given that the

box has an initial speed of4 m s-r and a finalspeed of 5 m s-1 at the end of the 6 m, what isthe friction between the box and the surface?

l0N6kg

A 2.ON

C 5.5NB 3.5ND 6.ON

4t Unit 7 Energy, Work and Power

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22. A box of 6 kg mass is being pulled up a

ramp by a force F at a constant speed as

shown. Given that the friction along the

surface is 4 N, what is the force F requiredto bring the box to the top of the ramp?(g=t0Nkg-')

6m 4 m

F

6kg

A4NC 44N

A 4NC 46N

6kg

AONC 12N

B 42ND 64N

)

()

B 4OND 64N

23. A box of 6 kg mass is being pulled up a

ramp by a force F from rest as shown. Given

that the friction along the surface is 4 Nand the flnal speed of the box on top of the

ramp is 2 m s r, what is the force F requiredto bring the box to the top of the ramp?(g=10Nkg')

6m

6kg

4

F

24. A box of 6 kg mass is being pulled bya 50-N force from an initial speed of4 m s-r at the foot of the ramp to a final speed

of 6 m s-r at the top of the ramp. What isthe magnitude of friction along the ramp?(g=t0Nkg-')

6m

B 4ND 5ON )

50

42

2ke

Unit 7 Energy, Work and Power

V* Abox is being pulled by an 8-N force as shown,

from an initial speed of 4 m s lat the foot ofthe ramp to a final speed of 6 m s-r at the topof the ramp. Given that the friction along the

ramp is 2 N, what is the mass of the box?(g=t0Nkg-')

8N

M 60" t------t-

5m

B 0.6 kg

D 2.4k9

V,

N

26. A box of mass 2 kg has an initial speed of10 m s I at the foot of the ramp. Given thatthe friction along the ramp is 2 N, calculate

the maximum height h that it can reach.(g=10Nkg')

10msl

2kg 60' t

A 0.2 kg

C t.Zkg

A 2.8mC 5.0m

A 2.5mC 4.5m

B 4.5mD 43.3 m

B 3.4mD 6.0m

)

()

()

h

27 . A box of mass 2 kg has an initial speed of10 m s Iat the foot of the ramp. Given that the

friction along the ramp is 2 N, calculate the

height ft that it reaches when the speed of the

box is 5 m s-1. (8 = l0 N kg-1)

l0 m s-l

60"

I

I

I

I

I

I

I

t

h

r -l-l-

J

| -l-l- i

I

I

I

I

I

I

I

I

I

I

I

t4I

I

I

I

I

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w,28. A box of mass 2 kg slides down from the topof the ramp with an initial speed of 0 m s-r.

Given that the friction along the ramp is 3.2 N,calculate the speed ofthe box when it reaches

the foot of the ramp. (S = l0 N/kg)

2ke

3m

m4

A 2.8 m s-'

C 8.0 m s-r

B 4.5 m s-t

D 8.9 m s-' ()

d

d

29. Abox is being pushed horizontally on a smooth

surface by a 10 N force for 6 m in 3 s. Whatis the power acting on the box during thisperiod?

lON r-----t T---------ttl

+------r-------)6m

A 5W B lSWc 20w D 600w

30. A man lifts a box of mass 2 kg verticallyupwards by 3 m. Given that he takes 6 s to do the

work, what is the power generated by the man?(g=10msa)

A lw B 6WclOw D360w ( )

31. A bullet hits a target board at a speed of300 m s 1. Given that the bullet is finallyembedded 3.0 cm into the target board and themass of the bullet is 15 g, what is the average

resistive force acting on the bullet while it ispenetrating into the target board?

A 225N B 2250Nc 22s00N D 225000N ( )

()

t\,s

U

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Wro

32. A 100 g mass drops from a 10 m building. Whatis the kinetic energy of the mass when it is 2 maway from the floor? (g = l0 m s-2)

AOJ B2Jc 8J D lOJ ( )

33. A 100 g mass drops from a l0 m building. Whatis the speed of the mass when it is 4 m awayfrom the floor? (g = 10 m s-2)

A 4ms-t B 6ms-tC 8ms-r D llms-' ( )

U

Vru.

A 1000 kg motorcar travels at a constant speed

of 30 m s-r along a road with frictional forceof 100 N. What is the power generated by themotorcar? (8 = l0 m s-2)

A 3000w B 4500wc 300000w D 4s0000w ( )

35. A motorcar of mass 500 kg generates a powerof l0 000 W How much time does the motorcarneed to accelerate from a speed of l0 m s-r to20 m s-1?

A 2.5 s B 5.0sC7.5s D10s ( )

U

A motorcar of mass 500 kg generates a powerof 10 000 W. Given that the total resistance onthe motorcar is 200 N, how much time does

the motorcar need to accelerate from a speed of10 m s-r to 20 m s-1?

A 6.3s B 8.3sC 9.2s D 10.7s ( )

37. A 100 W spotlight has an efficiency of 40Vo.

How much light energy can the spotlightproduce in an hour?

A t44kJ B 216kJc 360kJ D '720kJ ( )

43 Unit 7 Energy, Work and power

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38. A worm of mass 2 g crawls up a flight of steps

from point A to point B as shown. What is the

work done by the worm? (g = l0 N kg ')

2cm t 3cm

2cm t 3cm

^ I Cf{l t ---+3cm

<---'3cm

A 1.2 mJ

c 0.12t

B

A

39. A worm of mass 2 g crawls up a flight ofsteps from point A to point B as shown. Given

that the friction of the floor on the worm is

0.001 N, what is the work done by the worm?

2cm r 3cm

2cm t 3cm

^AI CITI r ---+3cm

<---)3cm

A 0.12 mJ

C 1.20 mJ

B 3.6 mJ

D I2OJ

B 0.18 mJ

D 1.38 mJ

()

()

B

A

The speed-time graph below shows the motion

of a motorcar on a level road within a l0 s

duration. Given that the mass of the motorcar

is 500 kg and the frictional force along the road

is 120 N, what is the power of the motorcar?

v/ms'

t2

4

tls

A 3200Wc 32000w

10

B 4160WD 41 600W

0

(

Vo,

Extension Questions

A mass of 2 kg is suspended by a 1.0 m longstring and is set free at point A as shown.Neglecting air resistance, what is the speed ofthe mass as it passes through point B?(8=10ms-2)

i

--*

l'---

I ,,'-l5--

B

A l.5ms-tC 3.2 m s-'

B 2.3 m s-t

D 4.1 m s-l (

U

Vo,

Uoo

42. A box of mass 3 kg is being pulled along a

horizontal bench at a constant speed of 5 m s-'

by a l0-N horizontal force. What is the workdone against friction in 4 s?

A OJ B 2OOT

c 600J D 1000J ( )

A block of mass rn slides from rest down a

smooth incline of length L. As a result, it moves

through a vertical height y, and a horizontaldistance x. When it reaches the bottom of the

incline, what is its kinetic energy?(Take acceleration due to gravity as g)

A mgL B *gyC (O.S)mx'z D (0.5)my2 ( )

Acar of mass lrt has an engine which can deliverpower P. What is the minimum time in which

the car can be accelerated from rest to a speed

v?

Amv

P

mv'

P

mv

2P,mv

B

D (

44

C2P

Unit 7 Energy, Work and Power

)

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1kg

A

A block of mass I kg has a speed of 20 m s-r at

point A. It is moving towards point C. Giventhat the frictional force along AB is 10 N and

the frictional force along BC is 5 N, what is thespeed of the block when it reaches point C andwhat is the time taken for the process? (Take

acceleration due to gravity to be l0 m s-2)

Height3m

3m 4m

C

Speed

A 15.2 m s-'

B 15.2 m s-'

C 17.0 m s-'

D 17.0 m s-'

Time taken

0.45 s

0.55 s

0.65 s

0.75 s ()

Vou. A bullet leaves the vertical barrel of a rifle and

reaches aheightof 720 m. What is the speed ofthe bullet when it leaves the barrel of the rifle toachieve this height? (Given that the acceleration

due to gravity is 10 m s-2)

A l20ms' B 170ms-1C 240ms-t D l4z00ms' ( )

N/U47. A cable car of mass 200 kg travels up a hill from

an altitude of 1030 m to an altitude of ll50 m.During this period, the cable car moves througha total of 250 m cable length in 5 min. What isthe rate ofincrease ofpotential energy?

A 800w B 1000wc 39500w D 48000w ( )

Wor.

Wo,

A block made from steel falls from position 1

to position 2 as shown. How much potentialenergy is lost during the process? (g = l0 m s-2,

density of steel = 8000 kg m')2m

2m

l0m

Position I

A I2.8 MJC 25.6MJ

A 0.5 m s-t

C l.7ms-t

Position 2

B 16.0 MJD 32.0 MJ

B l.l ms-rD 2.5 m s-l

(

A block resting on a smooth horizontal floor isbeing pushed by a constant horizontal force.

Find the following ratio:

Kinetic Kinetic Kineticenergy energy energy

gained in gained in gained inl" second 2nd second 3'd second

B l:4:9D l:1:1

A l:2:3C l:3:5 )

NVt)SO. e I kg mass and a 5 kg mass are held at a

position across a ramp as shown. Given thatthe friction along the ramp is 10 N, what isthe speed of the I kg mass after the masses

are released and the 1 kg mass has moved for10 cm?

5kg

lkgI

t l0cmi

()

45 Unit 7 Energy, Work and Power

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