Question

A coolie is pushing a box weighing $1500N$ up an inclined plane $7.5m$ long on to a platform, $2.5m$ above the ground.
(i) Calculate the mechanical advantage of the inclined plane.
(ii) Calculate the effort applied by the coolie.
(ii) In actual practice, the coolie needs to apply more effort than what is calculated. Give one reason why you think the coolie needs to apply more effort.

Answer 1

(i) Given : $l=7.5m,h=2.5m$.
Mechanical advantage (M.A.) $=\frac{l}{h}=\frac{7.5}{2.5}=3$
(ii) M.A. $=\frac{Load}{Effort}$
Effort $=\frac{Load}{M.A.}=\frac{1500}{3}$
Effort $=500N$.
(iii) In actual practice, due to some friction between the plane and the bottom face of the body which is pulled over it, the effort needed is certainly more than $L\sin \theta$, so the mechanical advantage is always less than $l/h$, hence, efficiency is less than $1$.