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 $80.5 \mathrm {~m} / \mathrm { s }$ 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.The vertical velocity of the ball when it is 89 m above the ground is closest to -81 m/s. This is because the ball is moving upward with an initial velocity of 80.5 m/s, and it has lost some of its velocity due to gravity. The acceleration due to gravity is 9.8 m/s^2, so the ball's velocity will have decreased by 9.8 m/s for every second that it has been in the air. Therefore, the ball's velocity when it is 89 m above the ground will be approximately 80.5 m/s - (9.8 m/s^2 * 10 s) = -81 m/s.

A Ball Is Projected Upward at Time T = 0 80.5 m/s80.5 \mathrm {~m} / \mathrm { s }80.5 m/s

A Ball Is Projected Upward at Time T = 0 $80.5 \mathrm {~m} / \mathrm { s }$