Unit 3Forces

1. The graph below shows how the velocity varieswith time for a given body.

velocity

0 time

Which of the following statement is/are true?I The resultant force acting on the body is

never zeto.II The forces acting on the body is never

constant for any period.III The object is never at rest.

A I and II B I, II and IIIC IIandIII D IIIonly ( )

2. P, Qand R are three identical blocks resting ona smooth surface. A force of 15 N is applied atone end as shown in the diagram below. What are

the tensions {, between blocks P and Q and Z,between blocks Qand R, in the strings?

T1 T2 15N

4. A constant force of magnitude 100 N acts on a

5 kg mass. If the mass starts from rest, what willits velocity be after 3 s?

A 60 m/s in the direction of the forceB 60 m/s opposite to the direction of the forceC 90 m/s in the direction of the forceD 90 m/s opposite to the direction of the force

()

5. Frve blocks, R q R, S and I of different masses

are connected by four identical strings 51, 52, 53

and So as shown. They are pulled by a steadilyincreasing force E Which of the following stringsis most likely to break?

Sa S3 S2 F

AC

s1

s3

B52DS,

3. A body is moving in a straight line under theaction of a constant force.What change will occurto the body?A Change in accelerationB Change in inertiaC Change in kinetic energ'yD Change in mass ( )

6. Two objects, A (of mass 3 kg) and B (of mass

2 kg), are stacked one on top of the other as

shown.

10N

Ifall surfaces are regarded as frictionless, thenthe acceleration of A in m s-2, when B is pulledby a force of 10 N, isA5 83.3c 2 D 0 (

7. You are told that both a 3 N horizontal force anda 4 N horizontal force are acting on an object, butyou are not told their directions. Based on thisinformation, what is the possible range for themagnitude.Fof the net force acting on the object?A 3sFs4 B 7sFs4C 3<lr<5 D lsFs7 ( )

TrA 15NB 5NC 1OND 7.5N

10N5N

7.5 N ()

T2

15N

w

()

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8. A constant horizontal force is applied to a bodyinitially at rest on a smooth horizontal table.Which of the following quantities will not change

during the application ofthe force?

A The displacement of the bodyB The velocity of the bodyC The acceleration of the bodyD The kinetic energy ofthe body ( )

9. Two blocks X and Y of weights 8 N and 2 Nrespectively are suspended by two strings as

shown. A downward force of 4 N is applied to Y.Frnd the tensions { and Z, in the two strings.

T1

4N

11. A balloon is acted upon by three forces, weight,upthrust and sideways force due to wind, as

shown in the diagram.

upthrust10 000 N

sideways force500 N

weight9000 N

What is the magnitude of the resultant force onthe balloon?A 5OON B 51ONc 1000N D 1120N ( )

72. An object is accelerating under the influence of a

force { on a frictionless surface. A while later, an

opposing force Frof the same magnitude acts onit. What will happen to the object?

F1

A The object will slow down.B The object will move at constant velocity.C The object will come to rest immediately

after the opposing force acts on it.D The objectwill move in the opposite direction.

()

13. Two forces of 30 N act simultaneously on a bodyof mass M.Which of the following arrangementswould produce the greatest acceleration?A soN 30N B 30N

30N

D 30N 30N

T2

TlA 8NB 1ONC 12ND 14N

xA 20NB lOONC 80ND 1OON

T2

22N4N6N6N

Y100 N20N80N80N

F1

,

10. Two forces act on an object. The forces are Xand Y. The object is moving in the horizontaldirection. Which values of A and B would cause

the object to move with constant speed?

X

()

C

30N30N

()

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14. Two strings are attached to an object at the 17

same point. They are each capable of sustaininga tension of 60 N and they subtend an angle of'J.20".

60N

What is the maximum weight they can support?A 3ON B 6ONceoN D120N ( )

15. The diagram below shows the top view of a fieldseparated into four sectors R Q, R, and S. A carttied to three ropes is placed in the middle of thefield. Three bull carts start to pull the ropes (withforces indicated in the diagram) at the same

time. In which sector will the cart start to moveinitially?

magnitude of forcesnot drawn to scale

A Sector PB Sector QC Sector RD Sector S

16. Why does an object falling in the Earthtgravitational field reach a steady velocity?A The mass of the object remains constant.B The weight of the object increases as it falls.C The Earth's gravitational field decreases as it

falls.D Air resistance increases with the increase of

velociry. ( )

A body of mass a.0 kg falls vertically through air.

When the magnitude of air resistance is 30 N,what is the acceleration of the body?

A 17.5 m s-2 B 7.5 m s)C 2.5ms2 D 0.4ms-2 ( )

18. When a mass starts moving from rest and a

constant force acts on it,I the acceleration is constant.II the velocity increases at a constant rate.III thedistance travelledis directlyproportionally

to the time.Which statement(s) is/are correct?A I only B I and II onlyC II and III only D I, II, and III

()

19. The velocity-time graph shows the motion of a

particle moving in a straight line.

velocity/m s-1

time/s

What may be deduced about the resultant forceacting on the particle during the first 2 s and after2s?

First2 s After2 s

A constant zeroB increasing at constant rate

a constant rateconstant lncreaslng at a

constant ratezero

constant rate

20. Abox of mass 2 kg moves with a constant speedof 0.1 m s-1 when a force of 6 N is applied.

0.1 m s-1+

6N

What is the frictional force acting on the box?A ON B 2Nc 3N D 6N ( )

N

20"

C

D at an increasing

weight

6N

P

S

5N

3N

o

R

()()

)_)

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27. The diagram below shows that two forces acting 24

at a point O are represented in magnitude and

direction OX and OY. The third force required tomaintain equilibrium is represented in magnitudeand direction by

22. Two forces P and Qact at a point X as shown in 26the vector diagram below.

X

In which of the following diagrams does the vector

F represent the resultant force ofP and Q!A B

o

P

23. When a block of mass 3 kg was pushed along a

surface with a force of 3 N, it moved with constant

speed.

When the same block was pushed with a force of9 N, what happened to the block?

A It moved with a constant speed of 2 m s-1 .

B It moved with a constant speed of 3 m s 1.

C It moved with a constant acceleration of2 m s-2.

D It movedwith a constant acceleration of 3 m s-2'

()

An astronautb boots weigh 100 N on Earth wherethe acceleration of free fall is 10 m s-2. How muchwill they weigh on Mars where the acceleration offree fall is 4 m s-2?

A 25N B 4ONc 100N D 400N ( )

25. A skater is pushing a snowmobile across an ice

rink. The skater pushed with a horizontal force

of 80 N and the snowmobile experiences a force

of friction of 30 N. The snowmobile has a

mass of 20 kg. What is the acceleration of the

snowmobile?A 4.0 m s-2 B 1.5 m s-2

C 2.5ms-2 D 0.25ms-2 ( )

An object of mass 5 kg is dropped from the topof a building. Which of the following statements

is true? (Neglect air resistance)

A It falls with a constant acceleration of 10 m s 2.

B It falls with a constant velociry of 10 m s-1.

C It falls with a constant acceleration of 20 m s-2.

D It falls with a constant velocity of 5 m s-1.

()

27 . Two forces of magnitude 8 N and 6 N act on the

same body.The angle betvveen the forces is 90".

What is the magnitude of the resultant of theforces?

A 7N B 1ONc14N D24N ( )

28. Three coplanar forces, of magnitude 20 N, 40 N,and 50 N, act on a body at P in the directionsshown in the diagram below.

North (bearing 0')

40N

20N 50NEast(bearing 90")(bearing 270')

Which one of the following is the approximate

bearing of the additional force required to maintain

equilibrium?A 37" B 127"

c 743" D 277" ( )

Z

XYYX

BD

OZZO

AC

PP

FF

PDC

o

F\

\

()

()

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29. When a horizontal force of 4 N is applied toa wooden block of mass 2 kg on a horizontalsurface, the block moves with a constant velocity.If the force is increased to 12 N, what will be theacceleration of the block?A 2ms'2 B 4ms2C 6ms2 D 8ms-2 ( )

30. A hammer hits a nail on a piece of wood with a

speed of 6 m s-1. If it drives the nail 0.L m intothe wood, what is the average deceleration of thehammer?A 18ms2 B 60ms-2C 1.20ms-2 D 180ms-2 ( )

31 . A 4.0 kg block ofwood is pulled along a horizontalground from rest, and a force on 15 N is requiredto produce an acceleration of2.0 m s-2.

What should the magnitude of the force be inorder to pull the block ofwood at constant speed

of 5.0 m s-1 on the same horizontal ground?A 5N B 7Nc 8N D 10N ( )

32. An empty lift of mass 200 kg is moving up with a

uniform velocity of 1.5 m s-1.

34. Forces of 2 N and 6 N act at a point. Which one

of the following could not be the magnitude oftheir resultant?A2N B4Nc 6N D 8N ( )

35. Two forces X and Y acting on a ball producea resultant force R on the ball. Which of thefollowing vector diagrams correctly represents theaddition of the force X and Y to produce R?

A Y B Y

x

C

x

36. Two forces, 4 N and 6 N, act on a body togive a resultant force I which of the followingstatements is true about F?

A F can be less than 2 N.B F can be greater than 10 N.C Fcanbe5N.D F can onlybe in one direction. ( )

37. 'Ihe diagram shows the velocity-time graph of anobject.

What can be said about the resultant force actingon the object?

A It is zero. B It is constant.C It is increasing. D It is decreasing.

()

RR

Y

x

DY

R

R

velocitv1.5 m 6-1

weight

Taking gravitational acceleration to be 10 m s 2,

what is the resultant force on the lift in newtons?A0 8200c300 D2000 ( )

33. When a block of mass 7.2 kg is pushed with a

horizontal force of 3 N along a horizontal flatsurface, it moves with a constant speed of 1.0 m s-1.

Howwill the block move when it is pushed alongthe same surface with a horizontal force of 9 N?A At a constant speed of 5 m s-1

B At a constant speed of 6 m s 1

C At a constant aiceleration of 5 m s-2

D At a constant acceleration of 6 m s-2

()

V

)(

I

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38. An object is moving in a straight line at 5 m s 1

when a constant force acts on it from the oppositedirection. Ifthe force is held constant for a longtime, how long will the object move?A It will stop moving immediately when the

force is applied.B It will decelerate and then stop.C It will decelerate, stop and then move in the

opposite direction with a constant speed.D It will decelerate, stop and then move

in the opposite direction with a constantacceleration. ( )

39. A ball of weight tr4/ slides along a smoothhorizontal surface until it falls offthe edge at timeT

o

Which graph represents how the resultant verticalforce ,F acting on the ball varies with time I as theball moves from position P to position QAFBF

40. A pendulum bob of weight WN,is suspended bya string from a point P. The bob is drawn aside bya horizontal force of 0.60 N so that the string istaut.

1.20 N30 cm

47. A rocket, launched vertically, receives a constantthrust throughout its ascent. Howeveq itsacceleration increases steadily as it goes up.Which one of the following reasons does NOTexplain the increase of acceleration?A The air resistance becomes smaller.B The total mass of the rocket is constantly

reducing.C The Earth's gravitational field becomes weakerD The atmospheric pressure becomes smaller.

()

42. '[he diagram shows a mass of 3.0 kg suspended

from tvyo bars of negligible mass connected byfive light strings. What tension in the stringlabelled X?

Bars ofnegligible mass

kg

P

cm40

P

0

C F D F

-W

W

TT

A 1.ONc 10.0 N

B 5.OND 15.0 N

The weight of the pendulum bob, in N, isA 0.45 B 0.60c 0.70 D 1.60 ( )

()

()

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43. Forces P and Q act at a point O as shown in thediagram below. The angle between their lines ofaction is fixed at angle 0, greater than 90" butlesser than 180".

44. Two loads, W, ar.d W, are attached to the ends ofa rope PQwhich is hung over a frictionless pulleyas shown in the diagram below.

P

o

If the magnitudes of P and Q can be varied, theline of action of their resultant can be made to lieI between the direction of P and OYII along the direction of OYIII between the direction of Q and OY

A I and II are possible.B I and III are possible.C II and III are possible.D I, II and III are possible. ( )

Frictionlesspulley

P

w1

o

W2

Load W, moves downwards when it is released

from rest. Which of the following statement is

true?A Load W, moves downwards with uniform

acceleration.B Load Wrmoves upwards with uniform velocity.C Tension in the rope equals to Wr.

D Tension in the rope equals to (W, + Wr).()

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