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.
Answer
Friction in moving parts of a machine reduces its efficiency.
A machine is a device that allows us to do work with less effort. Machines make our work easier to do. Machines have made our lives comfortable and faster.
It is a flat circular disc with a groove in its edge and a rope passing through the groove. It is capable of rotating around a fixed point passing through its central axis called axle.
A machine is 75% efficient’. What do you understand by this statement?
Answer
If a machine is 75% efficient, it means that 75% of the work input to the machine is obtained as the useful work output. The remaining 25% of the work input has been lost in overcoming the friction.
Can a machine have an efficiency of 100%? Give a reason to support your answer.
Answer
Efficiency of a machine is always less than 100% as output energy is always less than the input energy because some energy is lost to overcome friction.
Give a reason for the following. The efficiency of a machine is always less than 100%.
Answer
Efficiency of a machine is always less than 100% as output energy is always less than the input energy because some energy is lost to overcome friction.
Give a reason for the following. Machines are able to make our work convenient.
Answer
Machines help us to perform the same amount of work with much less effort than if we did the work manually. They also make our work faster and easier by multiplying the speed or the force applied.
Tools and objects that help us to perform the same amount of work with much less effort than if we did the work manually, are called machines. Example: lever, hammer, knife, etc.