A skateboarder moves at constant speed along a straight, level sidewalk. At time t=0 she releases a small steel ball from rest relative to herself, allowing it to fall toward the ground. A student standing on the sidewalk observes the motion of the ball.
Assume air resistance is negligible and all motion is confined to one dimension (horizontal forward is the +x direction, vertical downward is +y).
(a) Immediately after the ball is released, describe its velocity as measured by
(i) the skateboarder and
(ii) the student on the sidewalk. Include both magnitude and direction and provide reasoning for any differences you state.
(b) Suppose a third observer wishes to choose a reference frame in which the ball’s horizontal velocity is zero at the instant of release. Describe qualitatively how fast and in what direction that observer must move relative to the sidewalk. Explain your reasoning without performing numerical calculations.
(c) Compare the vertical acceleration of the ball measured by the skateboarder to that measured by the sidewalk student. Explain why the accelerations are the same or different, citing appropriate physical principles.