

Explanation
(a) Work is done whenever a force moves a body through a certain distance in the direction of the force. It is measured in joule and it is a scalar quantity.

(i) Minimum effort (E) applied in pulling up the box = F = mgsin\(\theta\) = 100 + 700 sin30° = 100 + 700 x 0.5 = 100 + 350=450N.
(ii) Velocity ratio (V.R) of the plane = 1/sin\(\theta\) - 5/2.5 = 2
(iii) Mechanical advantage of the plane (M.A) = L/E = 1.56 .
(iv) Efficiency of the plane = \(\frac{M.A}{V.R}\) x 100%
= \(\frac{1.56}{2}\) x 100% = 78%
(v) Energy lost in the system = work input - work output = (450 x 5) - (700/2 x 5) = 2250 - 1750 = 550J.
(vi) Work output of the man = mgh = 70 x 10 x 2.5 = 1750J
(vii) Total power developed by the man
= \(\frac{\text{work done by effort}}{time}\) = \(\frac{450 \times 5}{50}\) = 45 watts

