Exam Style Answers 5 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 5 7

Exam-style questions 1

B 

[1]

2

B 

[1]

3

a

Kinetic energy → heat (in the brakes)  [1]

 c

Loss of gra gravitational vitational potential energy →  gain in kinetic energy  [1] 8

4

a

=

horizontal distance moved  0.5  16 = 8.0 m  [1]

 

horizontal component of force = 200 cos 30° = 173 N 

[1]

work done = 173 × 8.0 =  1.39 × 103 J ≈ 1.4 kJ 

[1]

b 5

86.6 ≈ 87 W 

Truck: k.e. =  12 mv2 = 9.0 MJ 

[1]

1

p.e.. lost = mgh = 90 × 9.81 × 3.49  p.e

 

=

ii

  i

 

9

a

[1]

[1]

 3078 ≈ 3100 J  [1] 1 1 k.e. increase =  mv2 =  × 90 × 122  [1] 2 2 = 6480 J   [1]

c

 

wasted energy = power × time 

[1]

 

=

 2900 × 116.5 = 3.4 × 105 J 

[1]

Work is the product of force and distance moved. 

[1] [1] [1]

[1]

 

The distance moved is in the direction of the force.  [1]

b

i

As he falls, his potential energy decreases, his kinetic energy increases and internal energy (thermal energy/ heat) is produced as work is done against friction.  [1]

 

decrea se in p.e decrease p.e.. = increase in k.e. + internal energy produced 

[1]

 950 × 9.8 × 50 = 4.66 × 105 J ≈ 4.7 × 105 J   [1] work done time =    [1] power 5 4.6 66 6   × 10 t =  [1]  = 116.5 ≈ 120 s  4000 wasted power = 2.9 kW  [1]

 

 

 

[1]

The  T he dust particle has greater kinetic energy than the truck.  [1]

b

a

time taken

as work done against friction in the axle/chain or against air resistance.  [1]

so, work done  0 J  =

=

 

1 2 × 1100 × 18 2 =  = 7130 ≈ 7.1 kW  [1] 25   vertical distance = 40 sin 5° = 3.49 m  [1] i

gain in k.e.

 

[1]

 

power = 

[1]

Contact force acts at 90° to displacement 

mgh   gain in g.p.e. = mgh

c

Energy is wasted 

 iii iii

a

[1]

 ii ii

[1]

 Dust particle: k.e. =  mv  = 14 MJ  Dust

6

kinetic energy =  12   × mass × velocity2 

[1]

so, work done = 0 J 

2

b

 

 

1 2

[1]

energy produced by cyclist =  6480 − 3078 = 3402 J [1] energy  =  useful power output =  time 3402   67 power = 50.8 ≈ 51 W 

[1]

 

W 

b

Weight acts at 90° to displacement 

 ii ii

[1]

×

i

 

Rate at which work is done or work done/energy change per second 

 

Loss of gra gravitational vitational potential energy →  gain in kinetic energy  [1]

b

a

[1]

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

   

CAMBRIDGE INTERNATIONAL AS & A LEVEL PHYSICS: COURSEBOOK 

Graph with axes labelled and E p  decreasing linearly from 1000 J to 0  [1]

 ii ii

 

E k increasing from 0 when h = 0 

[1]

 

 

E k increases as a straight line to a value below 1000 J at h = 15 m 

[1]

Elastic p.e p.e.. is energy containe contained d in a stretched or squashed object. or When an object is raised above the Earth’s surface its gravitational p.e. increases. [1]

 

When a positively charged object is brought near another positively charged object its electric p.e. p.e. increases.  

ii

1000        J         /       y       g       r       e       n        E

E k

E p

b 15

10 a

 

[1]

since F  = ma and v2 = u2 + 2as and u = 0, s =  v2

2a

 

k.e. = ma ×

v2

2a

 = 

1 2

mv2 

b

i

 

11 a

2

2 =

i

mass = density × volume 6 10 = 1030 × 1.4 × 10  × 10.0 = 1.442 × 10   10 ≈ 1.4 × 10  J  [1]

 ii ii

Water falls an av average erage distance of 5.0 m when released through turbines.

 

p.e. lost = mgh =  p.e. 1.442 × 1010 × 9.81 × 5.0 (accept also also use of h = 10 m) 

[1]

  2 =

k.e.  mv      800  20    160 000 J 2   [1] energy 160000 = = 2.6 67 7 × 10 4 power =  time 6  2.7 × 104 W 

×

[1]

 

≈

 ii ii

Air resistance increases (with speed). [1]

 

Net driving force less or more energy (per second) wasted, so less availa vailable ble to increase k.e.  [1]

i

 iii iii

 

 

[1]

p.e.. lost = 7.07 × 1011 ≈ 7.1 × 1011 J p.e or

×

[1]

(Maximum [2])

1 =

[1]

 

h/m

k.e. = work done on body to increase speed from 0 to v = F  × s 

Gravitational p.e. is energy due to position in a gravitational field. 

×

12

=

(  1.4  10  J if h   10 used)  [1] energy output = 0.5 × (value in ii) 11 11 = 3.5 × 10  J (or 7.1 × 10  J if h = 10 used)  [1] energy 3. 5 ×1011 J power =   (or  = time 6 × 60 × 60 7.1  × 1011 J if h = 10 used)  [1] 6 × 60 × 60   power = 1.64 × 107 ≈ 1.6 × 107 W (or  3.3 × 107 W if h = 10 used)  [1]

The potential energy of a body is the energy stored in the body by reason of its position or shape shape..  [1]

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