Chapter 1

1

a)

8 m/s

2

a)

10 500 m (10.5 km)

b) 105 000 m (105 km)

c)

630 000 m (630 km)

4000 s (Snails can actually move faster than this! At a more realistic 4 mm/s (0.004 m/s) it would only take the snail 400 s or 6 minutes 40 seconds.)

4

a)

graph D

b) graph C

c)

graph A

d) graph B

a)

8m

distance

=

= 32 m/s

0.25s

time

The car is moving at constant velocity (speed).

5

IGCSE Physics Answers – Section A

3

6

gradient =

7

b) Time interval between first and seventh drip is 15 s (6

135 m ÷ 15 s = 9 m/s.

8

2.5 s) so average speed is

a)

1

b) Distance travelled is given by the area under the graph

= (5 s

20 m) + (0.5

5s

15 s)

= 137.5 m

9

a)

Average speed is found by dividing the total distance a body has travelled by the time it has taken; the speed may vary from moment to moment during this time. The instantaneous speed is the speed at which the body is travelling at a moment in time.

IGCSE Physics Answers – Section A

b) Speed is a scalar quantity – it is distance travelled divided by time without regard to direction. Velocity is a vector quantity – it is speed in a specified direction. 10 4 m/s2

11 a)

b)

c)

12 a)

3 m/s

b) 15 m/s

c)

13 a)

75 m/s

graph B

b) graph A

c)

graph D

d) graph C

2

14

a)

2.5 m/s2

b ) i)

20 m

ii)

50 m

c)

average speed = total distance travelled ÷ time taken.

IGCSE Physics Answers – Section A

15

= 70 m ÷ 9 s

= 7.78 m/s

16 The total distance travelled increases with the square of the time from the start, 0.5 m after 1 s, 2.0 m after 2 s, 4.5 m after 3 s, etc. Calculating the average velocity over each 1 s time interval (between the drips) and then plotting a graph of average velocity against time allows the acceleration to be calculated from the gradient of the graph. The acceleration is 1 m/s2.

Chapter 2

1

a)

gravity

b) friction

c)

normal reaction or contact force

2

Friction and air resistance (or viscous drag)

3

a)

1200 N

b) 1250 N

c)

50 N

d) red

4

3

IGCSE Physics Answers – Section A

5

6

a)

b) Any two sensible examples, such as: walking would be impossible without friction acting between your feet and the ground; climbing a rope would be impossible without friction acting between your hands and the rope.

7

a)

8

a)

b)

4

Without friction, objects would not be able to start moving from a stationary position, or stop moving when in motion. It would not be possible to build things because it would be difficult to pick up the building materials, and structures rely on friction to remain intact.

b)

a)

Load force on spring (newtons)

Length of spring (cm)

Extension of spring (cm)

0

5.0

0.0

2

5.8

0.8

4

6.5

1.5

6

7.4

2.4

8

8.3

3.3

10

9.7

4.7

12

12.9

7.9

b) c) (d – red line)

IGCSE Physics Answers – Section A

9

Chapter 3

1

A force that is not balanced by a force in the opposite direction. An accelerating car has an unbalanced force when the forwards force from the engine is bigger than the backwards force from air resistance.

2

From the equation force = mass acceleration (F = ma) we can see that if F, the thrust force of the rocket engines, is constant and m, the mass of the rocket, decreases then the acceleration must increase.

3

a)

F = ma, where mass = 0.5 kg and acceleration = 4 m/s2

So F = 0.5 kg

4 m/s2 = 2 N

b) m = F ÷ a, where force = 200 N and acceleration = 0.8 m/s2 So m = 200 N ÷ 0.8 m/s2 = 250 kg

c)

Use a = F ÷ m, where force = 250 N and mass = 25 kg

So a = 250 N ÷ 25 kg = 10 m/s2

4

By bending their legs and rolling on landing, parachutists extend the time over which their velocity is reduced to zero. This reduces the deceleration they undergo, and hence the forces that act on the body. Reducing the...