# Homework Help: Forces of girl on a sled

1. Oct 23, 2008

### hansel13

I'm not sure what the rules are about posting homework problems, but I just had 2 I couldn't get around too, so here's the second one...

1. The problem statement, all variables and given/known data
A 40 kg girl and a 8.4 kg sled are on the frictionless ice of a frozen lake, 15m apart but connected by a rope of negligible mass. The girl exerts a horizontal 5.2 N force on the rope.
What are the acceleration magnitudes of
(a) the sledge?
(b) the girl?
(c) How far from the girl's initial position do they meet?

2. Relevant equations
f=ma

3. The attempt at a solution
Finding the answers to part a and b were simple..
(a) a = f/m = 5.2N/8.4kg = .62 m/s2
(b) a = f/m = 5.2N/40kg = .13 m/s2
(c) I'm having problems figuring out part C.

2. Oct 23, 2008

### LowlyPion

Re: Force

Write equations for their positions
XG + XS = 15
XG = 1/2*ag*t2
XS = 1/2*as*t2

Solve noting that t2 is the same when they meet

3. Oct 23, 2008

### hansel13

Re: Force

1/2*ag*t2+1/2*as*t2= 15

t2 = 15 / (1/2*ag +1/2*as)
t2 = 15 / (1/2*.62 +1/2*.13)
t2 = 40
t = 6.3m

That doesn't seem right, I'm lost.

4. Oct 23, 2008

### LowlyPion

Re: Force

Not quite. That gives you seconds.

XG = 1/2*ag*t2 = 1/2*(.13)*(6.3)2 = 2.58m

5. Oct 23, 2008

### hansel13

Re: Force

ahh. Gotcha, thanks.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook