Help me please.. Suppose a car is moving in a straight line and steadily increases its
speed. It goes from 0 miles/hour to 15 miles/hour the first second and 15
miles/hour to 30 miles/hour the next second. What is the acceleration?

A)10 miles/hour/second

B) 15 miles/hour/second

C) 20 miles/hour/second

D)30 miles/hour/second

In an old-fashioned amusement park ride, passengers stand inside a 3.0-m-tall, 5.0-m-diameter hollow steel cylinder with their backs against the wall. the cylinder begins to rotate about a vertical axis. then the floor on which the passengers are standing suddenly drops away! if all goes well, the passengers will “stick” to the wall and not slide. clothing has a static coefficient of friction against steel in the range 0.60 to 1.0 and a kinetic coefficient in the range 0.40 to 0.70. part a what is the minimum rotational frequency, in rpm, for which the ride is safe? express your answer using two significant figures. f f = rpm