The figures below show four equal masses tied to a string being rotated on a frictionless horizontal surface. The relative values of their tangential velocities and radii of their circular motion are indicated. 21 Select one: B>C>A>D A B C D Which of the following ranks the tensions in the strings from highest to lowest? B>D>C>A D>A>C>B r/2 A>C>D>B 2v 2v

Problem 4 An amusement park ride consists of a large vertical cylinder that spins about its axis fast enough that any person inside is held up against the wall even when the floor is removed. The coefficient of static friction between the person and the wall is us = 0.3 and the radius of the drum is R = 2m. (a) Find wmin, the minimum angular speed at which the drum should rotate such that the person is held up even if the floor is removed. (hint: when the floor is removed, the person is held up by the static frictional force). (b) Find the linear speed of the person when the drum is rotating at the minimum angular speed you found in (a) (cC) Suppose that the drum started from rest and reached the speed you found in (a) in 120 seconds. During this time the drum had constant angular acceleration. Find the number of rotations made by the person within this time.

18. A car traveling on a flat (unbanked) circular track accelerates uniformly from rest with a tangential acceleration of 1.70-m/s. The car makes it one fourth of the way around the circle before it skids off the track. Determine the coefficient of static friction between the car and the track. Hint: you need to find the total acceleration of the car. Answer: 0.572