I was gone when my teacher assigned this, and now its spring break and i have no notes. Im sure they arent hard and all i am missing are equations. If anyone could help me that would be great :D(adsbygoogle = window.adsbygoogle || []).push({});

1. a .04 kg bullet is fired at a velocity of 1200 m/s from a 6kg gun. what is the recoild velocity of the gun

I think ive figured this out

V = -mv / M

so v = -(.04)(1200)/(6)

would be 8 m/s in the opposite direction :)

2. a 40 kg girl sits on a 15kg sled holding two 10kg bowling balls. Assuming the sled starts at rest on a frictionless horizontal surface, she throws the first ball backwards with a velocity of 4 m/s. then the second ball with the same velocity. What is the sled speed after the first ball is thrown? after the second ball?

Initial mass = 75 kg

after first ball 65 kg

after 2nd ball 55 kg

so initially you take v = -mv / M

v = -(10)(4)/(65) = .62 m/s

and for the 2nd ball you would use

v = -(10)(4)/(55) = .72 m/s

What i dont understand is how you calculate the final velocity for this problem.

3. A rocket can expel 200kg of mass per second at a velocity of 4000 m/s if the launce of the rocket requires an acceleration of 2.0 m/s, what is the greatest mass the rocket may be at the time of launch? (assume net mass of rocket is constant)

if i work this like a gun problem i get

V = mv / M

2 = (200)(4000)/ M

2M = (200)(4000)

M = 400000kg

4. a 8000 kg train travels north along a track at 3.0 m/s and collides with a stationary car of mass 13000 kg. if the cars couple and stick together, what is the final velocity of the two car system?

this one i think i know, using the equation

m1v1 + m2v2 = (m1 + m2) Vf

(8000)(3) + (13000)(0) = (8000 + 13000) Vf

24000 + 0 = 21000 Vf

Vf = 24000 / 21000 = 1.14 m/s

just want to make sure :)

5. a neutron (mass = 1.67 x 10tothe-27 kg( collides with a "resting" helium atom (mass = 6.64 x 10tothe-27 kg) at a celoxity of 2 x 10tothe6 m/s. The final velocity of the neutron is 1.8 x 10tothe6 m/s. What is the velocity of the helium atom, assuming the collision is in one dimension?

Thanks for any help i get :)

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# Homework Help: Conservation of momentum problems

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