Gravitational Field question

1. Jun 15, 2005

404

1. A person throws a ball upwards with a speed of 15 m/s, calc:
a) the time to the top of the trajectory (1.53s)
b) time the ball is in flight (3.06s)
c) max height of the ball (11.5m)

2. An astronaut is repairing top of her craft while docked on a strange new planet. ( ) She throws a tool down to her partner below at 2.5 m/s. Her partner catches the tool 2.86m below when it has reached a speed of 11.5m/s.
a) What is the gravitational field? (22 N/kg)
b) What is her weight if her mass is 58 kg? (1300 N)

I don't want the solutions, but can someone give me formulas I'm suppose to use for these questions? All I have in my notes is g=F/m...

2. Jun 15, 2005

whozum

The solution is more useful than just a formula. These shouldnt be just "look up the formula and plug it in", you should try to understand why they work, and if tehy dont, how to make them work.

For #1, use energy considerations to solve all three. The kinetic energy initially in the ball will do work against the gravitational field. It will gain potential energy until the KE is dispended, and at the point where KE is zero, the ball will be at its peak. Namely,

$$\frac{1}{2}mv^2 = mgh$$.

3. Jun 15, 2005

404

Well last time I asked for the solution was I given formulas so I thought I'd cut to the chase.

EDIT: ok number 1 worked out. Thanks

Last edited: Jun 15, 2005
4. Jun 15, 2005

404

Oh for Number 2a), I found acceleration to be 22m/s^2. The answer is 22N/kg, so maybe you assume she's dropping at maximum angle 90. a = g sin(theta), sin would be 1, so gravity comes out to be 22? I don't know... Just a crazy guess.

5. Jun 15, 2005

whozum

$$22 m/s^2 = 22 N/kg$$. If you don't see this, write out 1 Newton in terms of its base units (meters, seconds, kilograms). It says the object falls straight down, so we don't need to involve angles.

6. Jun 15, 2005

404

Ok, I see what you are saying now... Just making sure though, even though I included angles, was my thinking correct?

7. Jun 15, 2005

whozum

You didn't show me any thinking, you showed me an answer which matches the one you gave as correct earlier in a different form. I'm guessing that you did it correctly since you came to the correct answer without knowing it.