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Elastic and Inelastic Momentum Problem

  • Thread starter Dillion
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1. Homework Statement
A car whose mass is 2000 kg moves with a velocity of 30 m/s. It hits a stationary car that has the same mass. (Ignore all horizontal forces except for the ones that two cars exert on each other.)

a) The two cars stick to each other after the collision. What is their velocity after the collision?

b) In a different collision, with the same start, the cars do not stick to each other. After the collision the car that was originally at rest is observed to move with a velocity of 10 m/s at an angle of 35 degrees with the original motion of the other car. Find the momentum and velocity after the collision of the car that was originally moving.

2. Homework Equations

m2v2final + m1v1final = m2v2i + m1v1i

3. The Attempt at a Solution
for a) 2000v2+2000v1 = 2000(0) + 2000(30)
and since they stick together we can consider them one mass
4000Vf = 60000
vf = 15 m/s

for b) I don't know how to start because of the angle and it's inelastic because the cars do not stick together, right?

my attempt (but probably very wrong):

V2f - V1f = -(V2i - V1i)

10 - V1f = 30

V1f = -20 m/s ---> final answer for velocity

p = m x v

2000 kg x -20 m/s = 40000 kg m/s ----> final answer for momentum

I don't know where the angle comes into play.....
 

Doc Al

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for b) I don't know how to start because of the angle and it's inelastic because the cars do not stick together, right?
Remember that momentum and velocity are vectors. That's where the angle comes in: Divide things into components.

You might want to read this: Elastic and Inelastic Collisions
 

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