Conservation of Momentum Newton Collider
B) Recoil Problem - When interacting objects start from rest
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Ex 1) A 4.0 kg rifle fires a 5.0 x 10-3 kg bullet at a velocity of 500 m/s. What is the velocity acquired by the rifle? (no shooter)
After rifle is fired
Total Momentum Before =
0 = m1V1 + m2V2
Subtract m2V2 from both sides
m1v1 = - m2V2
In problem Solving, remove
(Not in Reference Table)
Ex 1) A 4.0 kg rifle fires a 5.0 x 10-3 kg bullet at a velocity of 500. m/s. What is the velocity acquired by the rifle?
(4.0 kg)V =(5.0x10-3 kg)500.m/s
(4.0 kg)V = 2.5 kgm/s
V = .63 m/s
Momenta before/after= 0 before
Equal Mass
Total momentum after = 0 ??
Yes, the slower cart has a greater mass
Ex 2) Two disk magnets are arranged at rest on a frictionless horizontal surface.
When the string holding them together is cut, they move apart under a magnetic force of repulsion.
a) What is the total momentum of the magnets before the string is cut? ![]()
Total momentum before = 0 (Both objects begin at rest)
b) What is the total momentum of the magnets after the string is cut?
Total momentum after = 0 (Total mom. before = Total mom. after)
c) What is the velocity of the 1.0 kg mass when the velocity of the 2.0 kg magnet is 30. m/s?
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m1 = 2.0 kg m2 = 1.0 kg V2 = ? V1 = 30. m/s
m1v1 = m2v2
2.0 kg(30. m/s) = 1.0 kg(V)
V = 60. m/s
m1v1 = m2v2
500 kg(V1) = 100 kg(15 m/s)
V1 = 3 m/s
Enrichment
Rifle Recoil
Georgia Public Broadcasting Momentum Video
ŠTony Mangiacapre., - All Rights Reserved
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