# Momentum when objects stick

1. Apr 30, 2007

### thomas49th

1. The problem statement, all variables and given/known data

A trolley of mass 2kg, travelling at 3m/s, collides with a stationary 1kg trolley. If the trolleys stick together, calculate:
a) the total momentum before thecollision
b) the speed of the two trolleys arter th collision

2. Relevant equations

momentum = mass x velocity
momentum before collision or explosion = momentum after collision or explosion

a collision is where equal forces act in opposite directions. An explosion is when objects
3. The attempt at a solution

how do i get B?

2. Apr 30, 2007

### mbrmbrg

You get part b using the second equation.

Total momentum before collsion=total momentum after collision.

The fact that the cart sticks tells you what about their velocities after they collide?

3. May 1, 2007

### thomas49th

if they collide and stick dont you add there masses to together so you have

2 x 3 = 2+1 x v

6 = 3 x v

6 / 3 = 2m/s

is that right?

4. May 4, 2007

### thomas49th

is the answer the right units as well? I presume the direction is always written as positive in the outcome?

5. May 4, 2007

### Staff: Mentor

Yes, your answer is correct in magnitude and units. But direction is irrelevant--all they ask for is the speed, which is always a postive number (or zero!).