# Homework Help: Weight physics course work

1. Oct 3, 2005

### CollegeMom

:grumpy: Okay I'm stuck...Here's the problem I'm dealing with:

An astronaut on another planet drops a 1-kg rock from rest and finds that it falls a vertical distance of 2.5 meters in 1 second. On this planet, the rock has a weight of:
a) 1 N b) 2 N c) 3 N d) 4 N e) 5 N

first of all which planet is "this planet?" does he want to know what it would weigh on Earth?

If the rate of free fall on Earth in 10 m/s squared, then would the force of gravity on the other planet be 1/4 of that at 2/5 m/s?

I'm not sure if I'm going in the right direction with this...how do I know what the force of gravity is on this other planet? If I know that wont I be able to relate that to 1-kg being equal to 10 N on Earth (as is 1-kg = 1.6 newtons on the moon because of gravity being 1/6 that of Earth)?

2. Oct 3, 2005

### Phymath

x = x_0 + v_0 t + 1/2 a t^2
-2.5m = 1/2 a (1 s)^2, a = -5 m/s^2

F_g (aka wieght) = mg = 1kg(5 m/s^2) = 5 N

3. Oct 4, 2005

### CollegeMom

Aha!

Okay...I get it!

So I use d=1/2gt^2

THANK YOU!!!