# How high does the ball rise?

1. Sep 12, 2009

### Leo34005

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

A tennis ball is shot vertically upward in an evacuated chamber(neglect air resistance) with an initial speed of 20m/s at time t=0s.

How high does the ball rise?

A)98.0m
B)72.4m
C)20.4m
D)10.2m
E)40.8m

Approximately how long does it take the tennis ball to reach its maximum height?

A)4.08s
B)9.08s
C)0.50s
D)6.08s
E)2.04s

2. Relevant equations

3. The attempt at a solution

2. Sep 12, 2009

### kuruman

3. Sep 12, 2009

### Leo34005

Its a freefall question regarding physics

4. Sep 12, 2009

### kuruman

And what do you know about free fall questions regarding physics? What are the relevant equations?

5. Sep 12, 2009

### Leo34005

Dont know anything. Would you mind?

6. Sep 12, 2009

### kuruman

7. Sep 12, 2009

### DrTravia

I learn the reasoning behind the equations, this lets you forget the equations formal setup while still being able to work it out

initial speed/gravity = time it takes to reach the top
so in this particular one it would be

20 divided by 9.8 (constant acceleration caused by gravity)

Take the time that you got and times it by the initial velocity and divide it by 2

(2.04 * 20) / 2

now this is a home-brew formula that i use to save some time when I don't need to be exact, itll be 0.1 off or somewhere around that area so if you need it to be exact then you need to do

(20*2.04)-(4.9*2.042)

20 is the initial velocity as he throws it up

2.04 is the time it takes for it to reach the top

4.9 is half of 9.8, which is the acceleration caused by gravity

the formula is

ymax = Velocityinitial*Time - 1/2Acceleration*Time2

Hope this amatuer helped out a bit.

Rise = C
Time = E