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GCSE Questions: Pressure, buoyancy, upthrust and fluids

Q8.

(a) A car has a total weight of 12000N.

It has four tyres each having an area of 25cm2 in contact with the road.

Calculate the pressure of the car on the road.

pressure = force ÷ area

P = F/A

12000 ÷ 100 OR 40000 ÷ 25

= 120 N/cm2

[4 marks]

(b) Seatbelts in cars are made of a wide material that stretches in a crash.

(i) Explain why it is important that the material is wide.

This reduces the pressure on the person held by the belt as it spreads the force over a larger contact area.

[1 mark]

(ii) Explain why it is important that the material is stretchy.

The stretchy material increases the time taken for the person to decelerate (change momentum) when the car brakes.

This reduces the force that the person experiences as Ft = Δp

[2 marks]

(c) Children in cars use special seats with their own seatbelts.

The seatbelts for children are narrower than adult seatbelts.

Why is it safe for children's seatbelts to be narrower than adult seatbelts?

The mass/inertia of child is lower so less force is needed for the same deceleration.

[2 marks]

(Total 9 marks)