Select the correct statement :
(a) A wheel barrow is a lever of class I.
(b) The efficiency of a machine is always 100%
(c) Friction in moving parts of a machine reduces its efficiency.
(d) No lever has the mechanical advantage greater than 1.
(e) It is easier to lift a load vertically up than to push it along an inclined plane.
(f) A screw is made by two inclined planes placed together.
Select the correct alternative :
Wheel is used with axle because
- sliding friction is less than the roffing friction
- rolling friction is less than the sliding friction
- they work as the inclined plane
- They help us to change the direction of force.