- #1

- 7

- 0

## Homework Statement

a. If a ball is launched straight upwards from the ground with an initial velocity of 20.0 m/s, how long does the ball take to reach a height of 15.0 m on the way up?

b. For the same situation, at what time does the ball reach 15.0 m on the way back down?

c. If a ball is dropped from a height of 100.0 m, what is it's height above the ground (in meters) after 3.0 s?

d. If a ball is dropped from a height of 100.0 m, what is it's velocity (in m/s) after 3.00 s? You may treat downward velocity as positive.

## Homework Equations

Vx = V0x + axt

x= x0 +v0xt + 1/2axt^2

## The Attempt at a Solution

a. 15 = 20t - 4.9t^2

I took the derivative of my equation.

15 = 20 - 9.8t

t = 0.510 s

b. 0 = 20t - 4.9t^2

I assume the height from problem a cancels out with problem b giving 0 and I also took the derivative of equation.

0 = 20 - 9.8t

t= 2.04 s

c. x = 100 - 4.9t^2

Plug in 3.0 s for t.

x = 55.9 m

d. Vx = 9.8 x 3.0 = 29.4 m/s