Exam Style Answers 3 Asal Physics CB

 

 

CAMBRIDGE INTERNATIONAL AS & A LEVEL PHYSICS: COURSEBOOK 

Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded may be different.

 Coursebook answers Chapter 3 3 ×10 3 m  

6

Exam-style questions

speed = 

−

1

D 

[1]

 

0.005 s 1 = 0.6 m s  

2

A 

[1]

b

speed = 

 

=

3

a

     

4

5

average acceleration 70

change in velocity   =  time

 = 140 × 103 m s 2  0.00 0005 05 average force = mass × acceleration   

=

−

[1] [1]

  a

weight = mass × g   g  

[1]

 

weight = 70 × 1.6 = 112 N 

[1]

b

resultant force = force up − force down  [1]

 

=

c

acceleration = 

 

388  = 5.54 =  70

a

At first, the only force is the weight,  [1]  but as its speed increases viscous drag increases.   [1]

 

b

 

[1] [1]

−

6000 m 3 ×10 3 s  

−

 

[1]

 2 × 109 m s 1 

[1]

−

speed = 

8 ×10

12

−

m

 

[1]

 

4 ×10 9 s 3 1 = 2 × 10  m s  

a

i

The Earth 

[1]

 ii ii

Upwards 

[1]

 iii iii

Gravitational force 

[1]

i

The Earth or the ground under the man  [1]

 ii ii

Downwards 

[1]

 iii iii

Contact force 

[1]

i

F  = ma = 1100 × 1.5 = 1650 N 

[1]

 ii ii

1650 + 600 = 2250 N (so that resultant force is still 1650 N)  

[1]

−

−

[1]

−

=

 500 − 112 = 388 N upwards  resultant force

mass m s  upwards 

7

b

[1]  

[1]

8

a

[1]

2

−

When viscous drag equals weight, the acceleration is zero and the speed is constant. 

9 [1]

Put rubber bands around the cylinder cylinder,, the same vertical distance apart along the cylinder.  [1]

 

Time the ball between the bands. 

 

When terminal velocity is reached, the time taken between successive bands will be constant.  [1]

 

c

[1]

 14 000 × 0.046 = 6440 N or 6.4 kN to 2 sig. figs  [1] weight mass =    [1]  g  mass = 6440 [1]  ≈ 660 kg  9.8

b

1

a

Starting and stopping the stopwatch involves random error. 

[1]

b

s = ut +  1 at2 =  12   × 1.5 × 102  2

[1]

 

s = 75 m 

[1]

a

1.5 m s 1 

[1]

b

Constant velocity is reached when weight = upward force due to air resistance   [1]

 

Air resistance increases with speed. 

 

Air resistance is less than the weight of the metal ball even at 2.5 to 3.0 m s 1  [1]

−

[1]

−

c

Initial acceleration is acceleration due to gravity or 9.81 m s 2  [1] −

 

Initially, neither ball has any air Initially, resistance. 

[1]

[1]

Cambridge International AS & A Level Physics – Sang, Jones, Chadha & Woodside © Cambridge University Press 2020

   

CAMBRIDGE INTERNATIONAL AS & A LEVEL PHYSICS: COURSEBOOK 

b

For example, body moves to the Moon or rises above the Earth  [1]

 

Amount of matter is constant, but force due to gravity is less on the Moon or at altitude  [1]

[1]

c

Mass: kg 

[1] [1]

  12 a

Weight: kg m s   [1] For a body of constant mass, the acceleration is directly proportional to the resultant or net force applied to it.  [1]

 

Directions of the acceleration and the resultant force are the same.  [1]

F  = ma = 1200 ×  82  

[1]

 

F  = 4800 N 

[1]

b

i

−

kg m s  

[1]

 ii ii

kg m 1 

[1]

 iii iii

4800 = b × 502 

 

b = 1.92 (kg m  or N s  m )  drag force = 1.92 × 302 = 1728 N 

10 a

2

−

1

−

 iv iv

 

2

−

2

2

−

acceleration = (4800 − 1728)/1200 =  2.6 m s 2  [1] −

v 

Sketch graph showing increasing gradient and force values marked at speeds of 0 and 50 m s 1  [1] −

 

11 a

2

[1]

Resistive force increases with speed, Resistive so resultant force and acceleration decrease.  [1] Mass is the amount of matter in a body. [1]

 

Weight is a force 

[1]

 

due to gravity acting on the body body.. 

[1]

b

i

It increases the time. 

[1]

 ii ii

If time increases then acceleration decreases.  [1]

 

Since F  = ma, when acceleration is less, the net force is less, and there is less force between the ground and the legs.  [1]

Cambridge International AS & A Level Physics – Sang, Jones, Chadha & Woodside © Cambridge University Press 2020