Part (a) was satisfactorily attempted by most candidates however; some confused work with moment of a
force. Part (b) was poorly attempted. Part (c) showed that lessons are probably presented in an abstract
manner as performance was poor. In part (d), the graph shape was correctly drawn by many but majority
quoted the formula F = ma instead of deducing it.

The expected answers are:

(a)(i) Work is the product ofa force (applied) and the distance moved in the __direction__ of the force

OR

The product of displacement and the component of the force in the direction of the displacement.

(ii) Power is the __time__ rate at which energy is expended.

OR

Power is the __time__ rate of doing work.

NOTE: Mathematical definitions are acceptable provided symbols are correctly defined.

(b) Any correct difference

e.g.

Static Friction |
Dynamic Friction |

It exists between surfaces of
stationary bodies |
It exists between surfaces in relative
motion |

- For the same system the static frictional force is greater than dynamic frictional force

(c) The tyres have treads in them to provide better grip of roads due to increased friction thus preventing vehicles from skidding

(ii) Retardation d = slope (oflast segment of graph)

= __v - 0__

T3 - t2

= __v__

t3 - t2

F = md

= Mv/t3 - t2