A body having a mass of 20 kg rests on a surface inclined 30° to the horizontal. Assume a
coefficient of friction of 0.76 and calculate the magnitude of the force F, acting at an angle of 40°
with the inclined surface required to:
a) Pull the body upwards;
b) Pull the body downwards;
c) Push the body upwards;
d) Push the body downwards.