(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 \(30\ \mathrm{ms}^{-1}\)...
(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 \(30\ \mathrm{ms}^{-1}\) for \(20\ \mathrm{s}\) was suddenly decelerated when the driver sighted a pot-hole. It took the driver \(6\ \mathrm{s}\) to get to the pot-hole with a reduced speed of \(18\ \mathrm{ms}^{-1}\). He maintained the steady speed for another \(10\ \mathrm{s}\) to cross the pot-hole. The brakes were then applied and the car came to rest \(5\ \mathrm{s}\) later. (i) Draw the velocity-time graph for the journey. (ii) Calculate the deceleration during the last \(5\ \mathrm{s}\) of the journey. (iii) Calculate the total distance covered.
(a) (i) Force is a push or pull which changes, or tends to change, the state of rest or uniform motion of a body in a straight line.
The S.I. unit of force is the newton (N).
(ii) The two types of solid friction are:
Static friction;
Dynamic (sliding or kinetic) friction.
(b) (i) Velocity-time graph
The successive points plotted are t time tand tvelocity tas follows:
\[(0,30),\ (20,30),\ (26,18),\ (36,18),\ (41,0).\]
Velocity-time graph showing constant speeds and uniform decelerations.