# Homework Help: Gravity Question (Grade 11)

1. Nov 10, 2009

### Fritsc

Questions;

1)A person in a hot air balloon at 500m is rising at 20m/s.
In order to rise up even faster, she drops her physics textbook out of the balloon.
How long will the book take to hit the ground?

Since it's thrown at 500m high, and Gravity is -9.8m/s
500/9.8 = 51 seconds
However I'm not pleased with the answer, I just feel something is missing and it should not be that easy.

2)A pop fly rises 80m after being hit by a bat.
How long is it in the hair before it is caught by the catcher?

Same logic.
80/9.8 = 8.1 seconds.

3)A ball is thrown up with a Vi of 30m/s^2 on the moon where gravity is 1/6g
How high?
How long total?
How long until ball is 100m high?

Moon gravity = 1.6

How high?
30/1.6 = 18.8s
1.6*18.8 = 30
30*18.8 = 564
564 - 30 = 534m

How long total?
30/1.6 = 18.8s

Hi there, I'm new to these forum, and new to physics!
These are some of the question that are given to me (There lots more!). But basically they're of the same concept so helping me with 3 of these will probably make me understand the rest of the question I'm given.

Thanks for the help!

Last edited: Nov 10, 2009
2. Nov 10, 2009

### therayne

Last edited by a moderator: Apr 24, 2017
3. Nov 10, 2009

### Fritsc

I've tried the question and I'm really confused right now!
I didn't type it out because it's a mess in my book.
Thanks!

4. Nov 10, 2009

### Redbelly98

Staff Emeritus
Welcome to PF

No, the acceleration due to gravity IS NOT -9.8 m/s, it is -9.8 m/s2

How about using the kinematic equations for motion with constant acceleration here?