## Q. 2.8

## Chapter 2

## Q. 2.8

Not a Bad Throw for a Rookie!

**GOAL** Apply the kinematic equations to a freely falling object with a nonzero initial velocity.

**PROBLEM** A ball is thrown from the top of a building with an initial velocity of 20.0 m/s straight upward, at an initial height of 50.0 m above the ground. The ball just misses the edge of the roof on its way down, as shown in Figure 2.20. Determine (a) the time needed for the ball to reach its maximum height, (b) the maximum height, (c) the time needed for the ball to return to the height from which it was thrown and the velocity of the ball at that instant, (d) the time needed for the ball to reach the ground, and (e) the velocity and position of the ball at t = 5.00 s. Neglect air drag.

**STRATEGY** The diagram in Figure 2.20 establishes a coordinate system with y_0 = 0 at the level at which the ball is released from the thrower’s hand, with y positive upward. Write the velocity and position kinematic equations for the ball, and substitute the given information. All the answers come from these two equations by using simple algebra or by just substituting the time. In part (a), for example, the ball comes to rest for an instant at its maximum height, so set v = 0 at this point and solve for time. Then substitute the time into the displacement equation, obtaining the maximum height.

**"Step-by-Step Explanation"**refers to a detailed and sequential breakdown of the solution or reasoning behind the answer. This comprehensive explanation walks through each step of the answer, offering you clarity and understanding.

Our explanations are based on the best information we have, but they may not always be right or fit every situation.

**blue check mark**means that this solution has been answered and checked by an expert. This guarantees that the final answer is accurate.

Learn more on how we answer questions.