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 because the ball is moving upward with a velocity of 80.5 m/s when it is 90 m above the ground. As it rises, its velocity decreases due to gravity. When it is 89 m above the ground, its velocity is slightly less than 80.5 m/s, but still positive. As it continues to rise, its velocity will continue to decrease until it reaches a maximum height, at which point its velocity will be zero. Then, it will begin to fall, and its velocity will increase in the downward direction. When it is 89 m above the ground on the way down, its velocity will be approximately -81 m/s.

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

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