A car of mass 1200 kg is travelling at 15 m/s. The driver brakes and the car stops.
Use the equation: kinetic energy=12×mass×speed2\text{kinetic energy} = \dfrac{1}{2} \times \text{mass} \times \text{speed}^2kinetic energy=21×mass×speed2
Calculate the energy in the kinetic store of the car before it brakes.
The brakes exert a constant braking force of 9000 N. All of the energy in the kinetic store of the car is transferred by the brakes.
Use the equation: work done=force×distance\text{work done} = \text{force} \times \text{distance}work done=force×distance
Calculate the braking distance of the car.
The same car is now travelling at 30 m/s. The braking force is the same.
Explain why the braking distance is four times greater.
The brakes get hot when the car stops.
Explain why.
50 exam-style questions on OCR GCSE Physics 8.1 Physics on the move, covering 8.1.1 Typical everyday speeds, 8.1.2 Typical everyday accelerations, 8.1.3 Ratios, units and rates on the road, 8.1.4 Human reaction times, 8.1.5 Factors affecting stopping distance, 8.1.6 Stopping distances at different speeds, 8.1.7 Dangers of large decelerations, 8.1.8 Estimating forces in road situations, and 8.1.9 Estimating the effects of large accelerations. Each one has a worked solution and a mark scheme showing where the marks go.