Q.21. Explain why scissors for cutting cloth may have blades longer then the handles, but shears for cutting metals have short blades and long handles.
A pair of scissors used to cut a piece of cloth has blades longer than the handles so that the blades move longer on the cloth than the movement at the handles.
While shears used for cutting metals have short blades and long handles because as it enables us to overcome large resistive force by a small effort.
(a) The weight W of the scale is greater than E.
It is because arm on the side of effort E is 30 cm and on the side of weight of scale is 10 cm. So, to balance the scale, weight W of scale should be more than effort E.
Q.23. Which type of lever has a mechanical advantage always more then 1 ? Give one example. What change can be made in this lever to increase its mechanical advantage?
Class II lever always have a mechanical advantage more than one.
Example: a nut cracker.
To increase its mechanical advantage we can increase the length of effort arm.
Q.24. Draw a diagram for a lever which is always used as a force multiplier. How is the effort arm related to the load arm in such a lever ?
In such a lever the effort arm is longer than load arm in such a lever.
Q.25. Explain why the mechanical advantage of a class II type of lever is always more then 1.
In these types of levers, the load L is in between the effort E and the fulcrum F. So, the effort arm is thus always longer than the load arm. Therefore M.A>1.