Some cars have an automatic emergency braking system. A sensor detects a hazard and the system applies the brakes 0.20 s later.
A car of mass 1200 kg travels at 22 m/s. A typical driver has a reaction time of 0.70 s.
Calculate how much shorter the thinking distance is when the automatic system applies the brakes instead of the driver.
The braking force on the car is 9600 N.
Calculate the braking distance of the car.
Use the equation
v2−u2=2×a×xv^2 - u^2 = 2 \times a \times xv2−u2=2×a×x
A child steps into the road 40 m in front of the car.
Determine whether the car stops before it reaches the child when braking is done by the driver and when braking is done by the automatic system.
Suggest one reason why the automatic system may not always stop the car in a shorter distance.
126 exam-style questions on Edexcel GCSE Physics 2.5 Stopping and braking distances, covering 2.5.1 Stopping distance and reaction time, 2.5.2 Factors affecting stopping distance, 2.5.3 Dangers of large decelerations, and 2.5.4 Braking distance and initial speed. Each one has a worked solution and a mark scheme showing where the marks go.