# Constant Acceleration in 1-D

1. Sep 21, 2015

### khzak1

1. The problem statement, all variables and given/known data

1. Rob throws a baseball upwards at 14.2 m/s. His friend, John, is sitting in a tree 4.5m above Rob.

a. Calculate how long it will take to reach John.

b. If John misses the ball as it moves upwards, how long will it take to reach John again.

2. Relevant equations
Δd=V(Δt) + 1/2 (a)(Δt)^2

3. The attempt at a solution
I have found the time using the quadratic equation for part a which is 0.36s, but I am stuck on part b. I do not understand how to do it. It seems like Δd is the same in both parts. How in hell do I find Δt for part b.

2. Sep 21, 2015

### haruspex

When you solve a quadratic, how many solutions do you get?

3. Sep 21, 2015

### khzak1

Well, you get 2 roots, but one is deemed useless because it is a negative.

4. Sep 21, 2015

### billy_joule

If you set up your equation correctly you'll get two positive roots, one being the 0.36 s you've found, and another at some later time.
Show your working and we'll see what went wrong.

5. Sep 21, 2015

### khzak1

-14.2 ± √113.35
-9.81

Δt=0.36s
Δt=-2.53s​

6. Sep 21, 2015