A small block on a frictionless horizontal surface has a mass of 2.50×10−2 . It is attached to a massless cord passing through a hole in the surface. (See the figure below .) The block is originally revolving at a distance of 0.300 from the hole with an angular speed of 1.75 . The cord is then pulled from below, shortening the radius of the circle in which the block revolves to 0.150 . You may treat the block as a particle.

Question

A small block on a frictionless horizontal surface has a mass of 2.50×10−2 . It is attached to a massless cord passing through a hole in the surface. (See the figure below .) The block is originally revolving at a distance of 0.300  from the hole with an angular speed of 1.75 . The cord is then pulled from below, shortening the radius of the circle in which the block revolves to 0.150 . You may treat the block as a particle.

drwls · Answer

There is no question here. Perhaps they want to know what happens to the angular speed of revolution. It speeds up by a factor of 4, to keep the angular momentum constant. The mass is not important; it cancels out of the angular momentum conservation equation.

Is the 1.75 in radians per second? If so, the answer is 7.5 radians per second.