68 - Rotational mechanics Questions Answers




No horizontal force.
Draw a perpendicular from centre to horizontal plane. Then calculate horizontal distance.
Now solve.
If any problem, then inform

In first case F = 2T = 150so T = 75 newton, Now in second case system is free to moveacceleration of the system a = F/20for 10 kg rod F-2T = 10a = 10(F/20) = F/2⇒F-(F/2)=2T ⇒F=4T = 300 newton
what is the moment of inertia of a cube about its diagonal?
Moment of inertia of a cube about a line perpendicular toits one face and passing through its centre is ma2/6so about diagonal inertia = l2Ix+m2Iy+n2Iz = (l2+m2+n2)Ix (here Ix=Iy=Iz)= Ix = ma2/6l,m,n are direction cosines of three lines passing througecentre of cube and perpendicular to each other


A rotating ball hits a rough horizontal plane with a vertical velocity and angular velocity . Given that the coefficient of friction is and the vertical component of the velocity after the collision is , find:
a) the angular velocity after collision;
b) the impulsive ground reaction during the collision
on applying momentum impulse theorem along vertical
-mv+Ndt = mv/2 (1)
by angular momentum angular impulse theorem
2mωr2/5 - μNdtr = 2mω,r2/5 (2)By eq. (2) get angular velocity.
impulsive ground reaction = √(Ndt)2+(μNdt)2by using eq. (1), solve it