# Help with Kinematics Physics problem

1. Dec 6, 2004

### BlasterV

Planet X.

Toss rock straight up in air at 17 m/s (initial speed).
After 14.2, the rock is falling towards him at 8.56 m/s

What is magnitude of the local gravitation acceleration?

Can someone show me how to do this, OR show me the equation for solving this type of problem? thanks

In terms of showing work, I can't even find an equation or an approach that I would be confident handing in as an answer, so I haven't gotten past the "how I approach this" point in the problem.

Last edited: Dec 6, 2004
2. Dec 6, 2004

### Spectre5

$$a=\frac{dv}{dt}$$

this is just about all you need to know to solve this problem...a first order linear differential equation with constant coefficients (remember signs)

3. Dec 6, 2004

### dextercioby

The formula is the correct one and the problem is simplified assuming constant gravitation field of intensity "g".Then
$$g=\frac{v_{0}+v_{f}}{t}}$$ which gives exactly 1.8 a bit more than the value on the moon.

4. Dec 6, 2004

### BlasterV

What units would the answer be in? I want to double check and make sure I got it right.

5. Dec 6, 2004

### dextercioby

I specifically left it without uniits,because i thought u specifically left time without units in the problem's text itself.It was some sort of a "payback".If those are seconds (it makes sense to think that way,in any unit system time's unit is second),then $g=1.8\frac{m}{s^2}$.If those were hours/days,then the assumption of constant gravitational field would not hold and the problem would be more compplicated than the author wanted.Or it could hold,but the intensty would be vanishingly small...

6. Dec 6, 2004

### BlasterV

erm, my bad, it is 14.2 seconds I must of missed it when copying the problem :/