(a) (i) Define force and state its S.I unit.
(ii) List the two types of solid friction.
(b) A car travelling at a constant speed of 30 ms-1 for 20 s was suddenly decelerated when the driver sighted a pot-hole. It took the driver 6 s to get to the pot-hole with a reduced speed of 18 ms-1. He maintained the steady speed for another 10 s to cross the pot-hole. The brakes were then applied and the car came to rest 5 s later.
(i) Draw the velocity-time graph for the journey.
(ii) Calculate the deceleration during the last 5 s of the journey.
(iii) Calculate the total distance covered.
Explanation
(a) (i) Definition of force
Action/push/pull that changes/tends to change the state of rest or of uniform motion in straight line. Its unit is newton (N)
(ii) Types of solid friction
– dynamic (friction)
– static (friction)
(b) (i) Velocity-time graph for journey