A tennis ball is thrown vertically upward with an initial ve

A tennis ball is thrown vertically upward with an initial velocity of +7.7 m/s. What will the ball\'s velocity be when it returns to starting point?

Answer in units of m/s. How long will the ball take to reach its starting point, and answer in units of s?

Solution

When the ball is thrown up it slows down as it goes up till it reaches a velocity = 0. At this time the ball starts to again fall down with increasing velocity in the opposite direction. In it\'s downward travel when it just crosses the starting point, its velocity is exactly equal to the original starting velocity, but in opposite direction.

Thus since the starting velocity of the ball u = 7.7 m/s

The final velocity when crossing the starting point during its fall will be v = -7.7 m/s.

the time \'t\' taken for the ball to accelerate from initial velocity to final velocity is given by the formula:

t = (v -u)/a

Where a = acceleration. As the ball is moving under the influence of earth\'s gravitation we know this to be = 9.81 m/(s^2).

Therefore: t = (v - u)/a = [7.7 -(-7.7)]/9.81 = 15.4/9.81 = 1.57 s (approximately)