Question

Why is MA affected by friction but not affected by VR

Answer 1

The question is wrong .
There is no relation between friction and VR . However to overcome friction greater effort is needed this decreases MA .but VR is not affected because it depends upon the displacement of load and effort and not on their magnitude . Hope you understood .

Answer 2

MA is known as Mechanical Advantage .

Mechanical Advantage is the ratio of load and effort.

Here both load and effort are forces .

Also friction is a force which is a opposing force and it opposes the load / effort and hence it can reduce the load / effort .

VR is velocity ratio .

Velocity ratio is the ratio of displacement of effort to load .

Here the displacement takes place.

Friction cannot reduce the displacement as it is only a force which is of opposing nature and thus VR is unaffected by friction.

So friction is responsible for lower the efficiency η .

Here η = MA / VR