# 47 - Rotational mechanics Questions Answers

Joshi sir comment
Joshi sir comment
Joshi sir comment

No horizontal force.

Draw a perpendicular from centre to horizontal plane. Then calculate horizontal distance.

Now solve.

If any problem, then inform

Joshi sir comment

what is the moment of inertia of a cube about its diagonal?

Joshi sir comment

Joshi sir comment

A rotating ball hits a rough horizontal plane with a vertical velocity $v$ and angular velocity $w$. Given that the coefficient of friction is $u$ and the vertical component of the velocity after the collision is $v/2$, find:

a) the angular velocity after collision;

b) the impulsive ground reaction during the collision

Joshi sir comment

on applying momentum impulse theorem along vertical

-mv+Ndt = mv/2       (1)

by angular momentum angular impulse theorem

By eq. (2) get angular velocity.

impulsive ground reaction = $\sqrt{{\left(Ndt\right)}^{2}+{\left(\mu Ndt\right)}^{2}}$by using eq. (1), solve it

What is the minimum coefficient of friction for a solid sphere to roll without slipping on an inclined plane of inclination θ?

Joshi sir comment

friction f = mgsinθ/[1+(mr2/I)]

solve for sphere and compare to μmgcosθ