A ball is projected upward at time t = 0 s,from a point on a flat roof 90 m above the ground.The ball rises and then falls with insignificant air resistance,missing the roof,and strikes the ground.The initial velocity of the ball is 80.5 m/s.Consider all quantities as positive in the upward direction.The vertical velocity of the ball when it is $89 \mathrm {~m}$ above the ground is closest to
A)-81 m/s.
B)-64 m/s.
C)-48 m/s.
D)-32 m/s.
E)-97 m/s.

Question

Quizplus · Accepted Answer

The correct answer is A.Explanation:The vertical velocity of the ball when it is $89 \mathrm {~m}$ above the ground is closest to -81 m/s. This is because the ball is moving upward with a velocity of 80.5 m/s at time t = 0 s, and its velocity will decrease as it rises due to the force of gravity. The ball will reach its maximum height when its velocity is 0 m/s, and then it will fall back to the ground with a velocity that is equal in magnitude but opposite in direction to its initial velocity. Therefore, the vertical velocity of the ball when it is $89 \mathrm {~m}$ above the ground is closest to -81 m/s.

A Ball Is Projected Upward at Time T = 0 89 m89 \mathrm {~m}89 m

A Ball Is Projected Upward at Time T = 0 $89 \mathrm {~m}$