Question

A puck on a horizontal, frictionless surface is attached to a string that passes through a hole in the surface, as shown in the figure(Figure 1). As the puck rotates about the hole, the string is pulled downward, bringing the puck closer to the hole.

a.) During this process, the puck's linear speed increases because _____. Explain.

b.) During this process, the puck's angular speed increases because _____. Explain.

c.) During this process, the puck's angular momentum remains the same because _____. Explain.

Answer 1

a] The string force is radial & exerts no torque on the puck so its angular momentum remains constants Because linear momentum L = mvr & r will decrease we conclude that the pucks linear speed will increase b] As stated above the angular momentum of the puck its moment of Inertia about the hok I = mr^2 will decrease Because angular momentum L = Iw & I will decrease we conclude that puck's angular speed will increase c] as stated above the angular momentum of the puck will stay the same because there is no torque on it