A disk rotstes at 70 r.p.m. in a horizontal plane. How would you place an object on the disk so that it would remain on it? The coefficient of static friction between the object and the disk is `mu^("stat")=0.44`.

Answer

At a distance less than 8 cm from the centre of the disk.

Explanation

In the case the object doesn.t slide off the disk, it will rotate with

the same angular speed as the disk. The centripetal acceleration is imparted to the object by the force of static friction (Fig.). We have
`m omega^(2)r le mu^("stat") mg, ` whence `r le mu^("stat") g//omega^(2)`