Consider a very low (zero) friction, 5.0 kg skateboard on a ramp at an angle of 15 degrees to the horizontal. what would be the net force that would cause the acceleration when the skateboard is allowed to move?
what would the skateboard's acceleration be down the plane?
now consider the same no-friction skateboard on the same 15 degree ramp. if a 45 kg teenager jumps on, what would be her acceleration down the ramp?

Review multiple-concept example 7 in this chapter as an aid in solving this problem. in a fast-pitch softball game the pitcher is impressive to watch, as she delivers a pitch by rapidly whirling her arm around so that the ball in her hand moves in a circle. in one instance, the radius of the circle is 0.626 m. at one point on this circle, the ball has an angular acceleration of 66.1 rad/s2 and an angular speed of 12.6 rad/s. (a) find the magnitude of the total acceleration (centripetal plus tangential) of the ball. (b) determine the angle of the total acceleration relative to the radial direction.