Force and Diagram

1

1

A wooden block of mass 0.60 kg is on a rough horizontal surface. A force of 12 N is applied to the block and it accelerates at 4.0 m s –2.
4.0 m s–2 wooden block

12 N

What is the magnitude of the frictional force acting on the block?
A
B

9.6 N

C

14 N

D

2

2.4 N

16 N

A submarine descends vertically at constant velocity. The three forces acting on the submarine are viscous drag, upthrust and weight.
Which relationship between their magnitudes is correct?
A
B

weight = drag

C

weight < upthrust

D

weight > upthrust

A ruler of length 0.30 m is pivoted at its centre. Equal and opposite forces of magnitude 2.0 N are applied to the ends of the ruler, creating a couple as shown.
2.0 N
50°
ruler

pivot
50°
2.0 N
What is the magnitude of the torque of the couple on the ruler when it is in the position shown?
A

0.23 Nm

B

0.39 Nm

C

0.46 Nm

D

0.60 Nm

Compiled nd rearrnged by Sjit Chandra Shakya

3

weight < drag

2

4

A ball falls from rest through air and eventually reaches a constant velocity.
For this fall, forces X and Y vary with time as shown.

force Y

force X

0

0

0

time

0

time

What are forces X and Y ? force X
A

air resistance

resultant force

B

air resistance

weight

C

upthrust

resultant force

D

upthrust

weight

The diagram shows four forces applied to a circular object.
30 N
20 N

20 N
30 N
Which of the following describes the resultant force and resultant torque on the object? resultant force

resultant torque

A

zero

zero

B

zero

non-zero

C

non-zero

zero

D

non-zero

non-zero

Compiled nd rearrnged by Sjit Chandra Shakya

5

force Y

3

6

A balloon is acted upon by three forces, weight, upthrust and sideways force due to the wind, as shown in the diagram. upthrust 10 000 N

sideways force
500 N

weight
9000 N
What is the vertical component of the resultant force on the balloon?
A

7

500 N

B

1000 N

C

10 000 N

D

10 500 N

The vector diagram shows three coplanar forces acting on an object at P.
3N
P
4N
4N

The magnitude of the resultant of these three forces is 1 N.
What is the direction of this resultant?

8

↓

B

↓

C

↓

What is meant by the weight of an object?
A

the gravitational field acting on the object

B

the gravitational force acting on the object

C

the mass of the object multiplied by gravity

D

the object’s mass multiplied by its acceleration

D

↑
Compiled nd rearrnged by Sjit Chandra Shakya

A

4

9

A uniform beam of weight 50 N is 3.0 m long and is supported on a pivot situated 1.0 m from one end. When a load of weight W is hung from that end, the beam is in equilibrium, as shown in the diagram. 3.0 m
1.0 m

W

pivot

What is the value of W ?
A

25 N

B

50 N

C

75 N

D

100 N

10 The diagram shows a sign of weight 20 N suspended from a pole, attached to a wall. The pole is kept in equilibrium by a wire attached at point X of the pole.

wire wall pole
X

SIGN
The force exerted by the pole at point X is F, and the tension in the wire is 40 N.
Which diagram represents the three forces acting at point X?

A

B

F
20 N
40 N

40 N
20 N

C

D
40 N

20 N
F

F
20 N

40 N

Compiled nd rearrnged by Sjit Chandra Shakya

F

5

11 An L-shaped rigid lever arm is pivoted at point P.
P
5N
2m
2m
10 N
1m

3m
20 N

Three forces act on the lever arm, as shown in the diagram.
What is the magnitude of the resultant moment of these forces about point P?
A

30 N m

B

C

35 N m

50 N m

D

90 N m

12 The vector diagram shows three coplanar forces acting on an object at P.
3N
P
4N
4N

The magnitude of the resultant of these three forces is 1 N.
What is the direction of this resultant?
B

C

13 A cyclist is riding at a steady speed on a level road.

D

Compiled nd rearrnged by Sjit Chandra Shakya

A

According to Newton’s third law of motion, what is equal and opposite to the backward push of the back wheel on the road?
A

the force exerted by the cyclist on the pedals

B

the forward push of the road on the back wheel

C

the tension in the cycle chain

D

the total air resistance and friction force

6

14 The diagrams show three forces acting on a body.
In which diagram is the body in equilibrium?
A

B

C

D

15 Two rigid rods, XZ and YZ, are fixed to a vertical wall at points X and Y.
A load of weight W is hung from point Z.
The load is not moving.

Z
X

W

load
Y

Which diagram shows the forces acting at point Z?
A

B

W

force in YZ

force in XZ

W

C

D

force in XZ

W

force in YZ

force in YZ

force in XZ

W

force in YZ

Compiled nd rearrnged by Sjit Chandra Shakya

force in XZ

7

16 A force F is applied to a beam at a distance d from a pivot. The force acts at an angle θ to a line perpendicular to the beam.
F
θ

pivot

d

Which combination will cause the largest turning effect about the pivot?
F

d

θ

A

large

large

large

B

large

large

small

C

small

small

large

D

small

large

small

17 A rigid uniform bar of length 2.4 m is pivoted horizontally at its mid-point.
0.8 m

0.8 m

200 N

300 N

Weights are hung from two points of the bar as shown in the diagram. To maintain horizontal equilibrium, a couple is applied to the bar.
What is the torque and direction of this couple?
40 N m clockwise

B

40 N m anticlockwise

C

80 N m clockwise

D

80 N m anticlockwise

18 Which of the following pairs of forces, acting on a circular object, constitutes a couple?
B

A
F

C

D

2F

F

F

F

2F
F
F

Compiled nd rearrnged by Sjit Chandra Shakya

A

8

19 An object has an initial velocity u. It is subjected to a constant force F for t seconds, causing a constant acceleration a. The force is not in the same direction as the initial velocity.
A vector diagram is drawn to find the final velocity v. u X v What is the length of side X of the vector diagram?
A

F

B

Ft

at

C

D

u + at

20 Two 8.0 N forces act at each end of a beam of length 0.60 m. The forces are parallel and act in opposite directions. The angle between the forces and the beam is 60 °.

8.0 N
60°

0.60 m
60°

8.0 N
What is the torque of the couple exerted on the beam?
A

2.4 N m

B

4.2 N m

C

4.8 N m

D

9.6 N m

21 A submarine is in equilibrium in a fully submerged position.

steel

sea water What causes the upthrust on the submarine?
A

The air in the submarine is less dense than sea water.

B

The sea water exerts a greater upward force on the submarine than the weight of the steel.

C

The submarine displaces its own volume of sea water.

D

There is a difference in water pressure acting on the top and bottom of the submarine.

Compiled nd rearrnged by Sjit Chandra Shakya

air

9

22 A uniform ladder rests against a vertical wall where there is negligible friction. The bottom of the ladder rests on rough ground where there is friction. The top of the ladder is at a height h above the ground and the foot of the ladder is at a distance 2a from the wall.
The diagram shows the forces which act on the ladder.

F ladder h
W

W

a

F a Which equation is formed by taking moments?
A

Wa + Fh

= 2W a

B

Fa + Wa

= Fh

C

W a + 2W a = F h

D

W a – 2W a = 2F h

23 A spanner is used to tighten a nut as shown.

0.04 m
0.25 m
F = 200 N

What is the resistive torque, in an anticlockwise direction, preventing further tightening?
A

8Nm

B

25 N m

C

50 N m

D

800 N m

Compiled nd rearrnged by Sjit Chandra Shakya

A force F is applied at right-angles to the spanner at a distance of 0.25 m from the centre of the nut. When the nut is fully tightened, the applied force is 200 N.

10

24 A uniform metre rule of mass 100 g is supported by a knife-edge at the 40 cm mark and a string at the 100 cm mark. The string passes round a frictionless pulley and carries a mass of 20 g as shown in the diagram.

0

40

20

60

80

100

20 g
At which mark on the rule must a 50 g mass be suspended so that the rule balances?
A

4 cm

B

36 cm

C

44 cm

D

96 cm

25 A car of mass 750 kg has a horizontal driving force of 2.0 kN acting on it. It has a forward horizontal acceleration of 2.0 m s–2.

resistive force driving force

What is the resistive force acting horizontally?
A

0.5 kN

B

1.5 kN

C

2.0 kN

D

3.5 kN

What is the order of increasing magnitude of these three forces?
A

upthrust → viscous drag → weight

B

viscous drag → upthrust → weight

C

viscous drag → weight → upthrust

D

weight → upthrust → viscous drag

Compiled nd rearrnged by Sjit Chandra Shakya

26 A ball is falling at terminal speed in still air. The forces acting on the ball are upthrust, viscous drag and weight.

11

27 A hinged door is held closed in the horizontal position by a cable.
Three forces act on the door: the weight W of the door, the tension T in the cable, and the force H at the hinge.

cable

wall

T door hinge

H
W

Which list gives the three forces in increasing order of magnitude?
A

H,T,W

B

T,H,W

C

W,H,T

D

W,T,H

28 Two parallel forces, each of magnitude F, act on a body as shown.

F

d

F

What is the magnitude of the torque on the body produced by these forces?
A

Fd

B

Fs

C

2Fd

D

2Fs

Compiled nd rearrnged by Sjit Chandra Shakya

s

12

29 The diagram shows four forces applied to a circular object.
45 N
30 N

30 N
45 N

Which of the following describes the resultant force and resultant torque on the object? resultant force

resultant torque

A

non-zero

non-zero

B

non-zero

zero

C

zero

non-zero

D

zero

zero

30 The diagrams represent systems of coplanar forces acting at a point. The lengths of the force vectors represent the magnitudes of the forces.
Which system of forces is in equilibrium?
A

B

C

D

0.5 m

2.5 m

beam

pivot

300 N

What is the weight of the beam?
A

300 N

B

480 N

C

600 N

D

960 N

Compiled nd rearrnged by Sjit Chandra Shakya

31 A long uniform beam is pivoted at one end. A force of 300 N is applied to hold the beam horizontally. 13

32 Which two vector diagrams represent forces in equilibrium?

P

R

A

Q and R

C

R and S

D

S

P and Q

B

Q

S and P

33 What is meant by the weight of an object?
A

the gravitational field acting on the object

B

the gravitational force acting on the object

C

the mass of the object multiplied by gravity

D

the object’s mass multiplied by its acceleration

34 A uniform beam of weight 100 N is pivoted at P as shown. Weights of 10 N and 20 N are attached to its ends.
The length of the beam is marked off at 0.1 m intervals.
At which point should a further weight of 20 N be attached to achieve equilibrium?

0.1 m

A

B

C

D

P
10 N

20 N

Compiled nd rearrnged by Sjit Chandra Shakya

0.4 m

0.6 m

14

35 The diagram shows a cannon ball fired from a cannon. cannon cannon ball The mass of the cannon is 1000 kg and the mass of the cannon ball is 10 kg.
The recoil velocity of the cannon is 5 m s–1 horizontally.
What is the horizontal velocity of the cannon ball?
A

B

200 m s–1

500 m s–1

C

2000 m s–1

D

5000 m s–1

36 A block of mass 0.60 kg is on a rough horizontal surface. A force of 12 N is applied to the block and it accelerates at 4.0 m s –2.
4.0 m s–2 block 12 N

What is the magnitude of the frictional force acting on the block?
A

B

2.4N

5.3 N

C

D

6.7 N

9.6 N

38 A wooden block rests on a rough board. The end of the board is then raised until the block slides down the plane of the board at constant velocity v. block v

Which row describes the forces acting on the block when sliding with constant velocity? frictional force on block

resultant force on block

A

down the plane

down the plane

B

down the plane

zero

C

up the plane

down the plane

D

up the plane

zero

Compiled nd rearrnged by Sjit Chandra Shakya

board

15

39 Three coplanar forces, each of magnitude 10 N, act through the same point of a body in the directions shown.
10 N

10 N
30o 30o

10 N

What is the magnitude of the resultant force?
A

B

0N

C

1.3 N

D

7.3 N

10 N

40 Which force is caused by a pressure difference?
A

friction

B

upthrust

C

viscous force

D

weight

41 A car with front-wheel drive accelerates in the direction shown.

A

B

C

D

Compiled nd rearrnged by Sjit Chandra Shakya

Which diagram best shows the direction of the total force exerted by the road on the front wheels? 16

42 A rigid circular disc of radius r has its centre at X. A number of forces of equal magnitude F act at the edge of the disc. All the forces are in the plane of the disc.
Which arrangement of forces provides a moment of magnitude 2Fr about X?

A

B

F

X

X

F
F

C

D
F
X

X
F

F
F

F

43 The diagram shows a plan view of a door which requires a moment of 12 N m to open it. door wall

wall
0.80 m

hinge

What is the minimum force that must be applied at the door’s midpoint to ensure it opens?
B

4.8 N

C

9.6 N

D

15 N

30 N

44 Which pair of forces acts as a couple on the circular object?
A

C

B
F

F

D

2F
F

F

2F
F

F

Compiled nd rearrnged by Sjit Chandra Shakya

A

17

45 Which two vector diagrams represent forces in equilibrium?

R

A

P and Q

B

Q

S

Q and R

C

R and S

D

S and P

Compiled nd rearrnged by Sjit Chandra Shakya

P