Question

Two kids are roller skating. Amy, with a mass of 55 kg, is traveling forward at 3 m/s. Jenny, who has a mass of 40 kg, is traveling in the opposite direction at 5 m/s. They crash into each other and hold onto each other so that they move as one mass. How fast are they traveling?

I'm so confused please help.

Answer 1

velocity = mass * acceleration

Answer 2

this is an exercise conservation of momentum
The total momentum before the crash = total after the crash.

Momentum = mass * velocity

Answer 3

Thanks.

Answer 4

note that momentum is a vector so that if you take Jenny's velocity to be 5 m/s then Amy's velocity will be -3 m/s

Answer 5

do you need any more help?

Answer 6

Hold on, I'm gonna try to answer it and then I'll ask if I did it right.

Answer 7

fine

Answer 8

Okay. So
Amy
55 * 3 = 220 N
Jenny
40 * 5 = 200 S


Do I subtract those two to get the answer?

Answer 9

55 * 3 = 165

Answer 10

Oops. Thanks for catching that.

Answer 11

You add these 2 values
220 + (-165)
this is the totalmomentum before the collision
After the collision the mass of the 2 girls = 85 kg so that the momentum is 95v where v is their velocity

So equate these 2 and solve for v

Answer 12

* Sorry that's 95 kg not 85

Answer 13

Okay. Thanks a ton!!!

Answer 14

yw