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GCSE Questions: Forces

Q29. The thinking distance and braking distance for a car vary with the speed of the car.

(a) Explain the effect of two other factors on the braking distance of a car.

Do not refer to speed in your answer.

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 2:

Relevant points (reasons / causes) are identified, given in detail and logically linked to form a clear account.

3 - 4 marks
Level 1:

Points are identified and stated simply, but their relevance is not clear and there is no attempt at logical linking.
1 - 2 marks
Level 0:

No relevant content
0 marks

 

Indicative content:

Factors affecting friction between the car and the stopping surface

• poor condition of tyres

• poor road surface

• wet or icy road

• poor/worn brakes

Explanation to be given:

• because of decreased friction braking distance will increase

Factors increasing the mass of the vehicle

• increased mass of car due to passengers or carrying a load

Explanation to be given:

• increased kinetic energy and/or momentum of the car happens when mass is increased and therefore requires more work to be done by the brakes to stop the car - increasing braking distance.

Factors affecting the gradient of the surface

• road slopes downhill makes braking distance increase

• road slopes uphill makes braking distance decrease

Explanation to be given:

• (a component of) gravity opposes/assists the braking force therefore the resultant (braking) force is increased/reduced.

A single factor with no related explanation was consideredinsufficient to score a mark.

[4 marks]

(b) The mean braking force on a car is 7200 N.

If the car has a mass of 1600 kg calculate the deceleration of the car.

F = ma

7200 = 1600 x a

a = 7200/1600

a = 4.5 m/s2

[4 marks]

(c) The graph below shows how the thinking distance and braking distance for a car vary with the speed of the car.

Determine the stopping distance when the car is travelling at 80 km/h.

Stopping distance = thinking distance + braking distance

Stopping distance = 15 + 38

Stopping distance = 53 m

[3 marks]

(d) The diagram shows part of the braking system for a car.

When the brake pedal is pressed, a force of 60 N is applied to the piston.

The pressure in the brake fluid is 120 kPa.

Calculate the surface area of the piston.

Give your answer in standard form to 2 sf.

Pressure = Force/Contact Area

P = F/A

120 x 103 = 60/A

A = 60/(120 x 103)

A = 5.0x 10-4 m2

[5 marks]

 

[16 Marks TOTAL]