A ball is thrown vertically upwards at 19.6 m/s.For its complete trip (up and back down to the starting position),its average speed is:

A) 14.7 m/s.
B) 9.8 m/s.
C) 19.6 m/s.
D) 4.9 m/s.
E) not given.

Question

A ball is thrown vertically upwards at 19.6 m/s.For its complete trip (up and back down to the starting position),its average speed is:
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A) 14.7 m/s.
B) 9.8 m/s.
C) 19.6 m/s.
D) ​4.9 m/s.
E) ​not given.

Quizplus · Accepted Answer

The ball will follow a projectile motion, reaching its maximum height when its vertical velocity becomes zero and then falling back to the starting position with the same initial velocity. The time to reach the maximum height is given by t=V₀/g, where V₀ is the initial vertical velocity and g is the acceleration due to gravity. Thus, t=19.6/9.8=2 seconds.
The maximum height reached by the ball is given by h=V₀² /2g=19.6² / (2 x 9.8) =19.6 meters.
The time to complete the round trip (up and back down) is t_total=2t=4 seconds, since the motion is symmetrical. Therefore, the total displacement of the ball is zero, and the average speed is simply the total distance traveled divided by the time taken, which is 2h/t_total = 39.2/4=9.8 m/s. Hence, the answer is (B) 9.8 m/s.

A Ball Is Thrown Vertically Upwards at 19