NDA 1 2024 GAT, question 88

Topic: Physics

Q88

Which one of the following about different frictional forces is correct ?

(a) $\text{Kinetic friction}>\text{Static friction}>\text{Rolling friction}$
(b) $\text{Static friction}>\text{Rolling friction}>\text{Kinetic friction}$
(c) $\text{Static friction}>\text{Kinetic friction}>\text{Rolling friction}$ Correct answer
(d) $\text{Static friction}>\text{Kinetic friction}=\text{Rolling friction}$

Solution.

Answer: (c) $\text{Static friction}>\text{Kinetic friction}>\text{Rolling friction}$

It takes more force to start an object sliding (static friction) than to keep it sliding (kinetic friction).
Rolling causes much less friction than sliding.
So static > kinetic > rolling.

Trap: "Static friction" here means its maximum (limiting) value; below that limit static friction is only as large as the applied force.