Give reasons for the following statements.

(a) Work done by a standing man is zero.

(b) A simple machine neither provides energy nor does any work.

(c) Mechanical advantage of class II lever is always greater than 1.

(d) Effort depends on the steepness of inclined plane.

(e) Efficiency of a machine cannot be 100%.

(a) Work done by an object is the product of force and distance i.e.,

Work = Force x Distance

Since the man is standing so no distance is covered by him even after applying muscular force to counter gravitational pull of the earth and hence, no work is done by the man.

(b) A simple machine works on an object only when we do some work on it by applying force. Therefore, a simple machine neither provides energy nor does any work on its own.

(c) As, mechanical advantage of a lever is given by the ratio of the effort arm to the load arm i.e.,

$\text {Mechanical Advantage (M.A.)} = \dfrac{\text {Effort arm}}{\text {Load arm}}$

In class II lever, the effort arm is always longer than the load arm i.e.,

Effort arm > Load arm

$\Rightarrow \dfrac{\text {Effort arm}}{\text {Load arm}} \gt 1 \\[1em] \Rightarrow \text {Mechanical Advantage (M.A.)} \gt 1$

Hence, mechanical advantage of class II lever is always greater than 1.

(d) The mechanical advantage of an inclined plane is equal to the ratio of the length of the inclined plane to its vertical height i.e.,

$\text {Mechanical Advantage (M.A.)} = \dfrac{\text {Length of the inclined plane (L)}}{\text {Vertical height (h)}}$

Higher the value of h, steeper is the slope. Hence, effort depends on the steepness of inclined plane.

(e) The efficiency of every machine used by us is always less than 100% because some of the input energy is used up in overcoming the friction between different parts of the machine and as heat from the working parts of the machine. Therefore, output energy is always less than the input energy.