A ping pong ball is rolling across a table at 2.1 cm/s. When the ball is 1.32 m away from the edge your little brother starts to blow on it. If the little doofus hopes to prevent the ball from falling off the edge, what minimum acceleration must be achieved?
the final velocity of the ball must be zero at the edge of the table (after 1.32 m of travel)
the average velocity is initial plus final,divided by two
v = (2.1 cm/s + 0 cm/s) / 2 = 1.05 cm/s
the time to stop the ball is the distance divided by the velocity
t = 132 cm / 1.05 cm/s = 126 s
the necessary acceleration is the change in velocity divided by the time
a = -2.1 cm/s / 126 s