10 13 The photograph shows a model racing car set. The curved parts of the track are semicircular. The car makes electrical contact with the track using metal brushes underneath the car. (a) There is a maximum speed for the car to stay on the curved part of the track. Explain why the car will slip off the curved part of the track if the car exceeds the maximum speed. (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (b) The following measurements are made for a car starting at rest on a straight piece of track. distance travelled = 1.2 m time taken = 0.77 s (i) Show that the final velocity of the car is about 3 m s−1. Assume the acceleration is constant. (2) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. 11 Turn over (ii) The final velocity calculated in (b)(i) is the maximum velocity before the car slips off the track. Calculate the maximum horizontal force between the curved part of the track and the car. mass of car = 0.050 kg radius of curved part of track = 0.042 m (2) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Maximum horizontal force = ...................................................... (c) The cars are controlled separately and so can be raced, with one car on the inner lane and the other on the outer lane. The cars are identical. Each car is raced at its highest speed for that lane. Explain why the outcome of the race is difficult to predict. (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (Total for Question 13 = 10 marks)