# Homework Help: Calculation of Velocity in reference to circular motion

1. Sep 18, 2008

### Kdoll1

1. The problem statement, all variables and given/known data
1. A boy with a mass of 50kg jumps off a 30kg boat, causing the boat to move to the right at 2 m/sec. What did the boy jump with a velocity of?
a.-1.2 m/sec
b.3.3 m/sec
c.1.1 m/sec
d.0.2 m/sec
e.-3.3 m/sec

2. A 2kg cart moving in a straight line hits a piece of modeling clay that has a mass of 1kg and is at rest. After the collision, the cart and clay stick together and move at 1m/sec to the left. The initial velocity of the cart is ___m/sec to the left.
a.1
b.1.5
c.2
d.2.5
e.-0.33

2. Relevant equations

m1*v2/r=g*m1m2/r2.....all of those numbers are subscripts

3. The attempt at a solution
1. v=sq. root of Gm/r
v=(6.67*10^-11)20/2=
1.334*10 to the second

2. 1/3

I am beyond confused....physics does not click in my head at all.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Sep 19, 2008

### alphysicist

Hi Kdoll1,

This equation describes the motion of satellites, which would not apply here, and the problems you posted do not deal with circular motion. Instead, the problems deal with conservation of momentum, so what is going wrong is you are using the wrong approach. So read the conservation of momentum section and try them again, and see if you can get the answer.