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songoku
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Homework Statement
A 1000 kg car with 4 people on it, each 75 kg, is at rest. The people jump off the car with speed 2 ms-1 relative to the car. Find the speed of the car if the people jump off :
a. simultaneously
b. one by one
Homework Equations
conservation of momentum
The Attempt at a Solution
a.
m1u1 + m2u2 = m1V1 + m2V2
0 = 300 * 2 - 1000 * v2
v2 = 0.6 ms-1b.
(i) when person 1 jumps off :
m1u1 + m2u2 = m1V1 + m2V2
0 = 75 * 2 - 1225 * v2
v2 = 6/49 ms-1
(ii) when person 2 jumps off :
m1u1 + m2u2 = m1V1 + m2V2
0 = 75 * (2 + 6/49) - 1150 * v2
v2 = 156/1127 ms-1
(iii) when person 3 jumps off :
m1u1 + m2u2 = m1V1 + m2V2
0 = 75 * (2 + 156/1127) - 1075 * v2
v2 = 7230/48461 ms-1
(iv) when person 4 jumps off :
m1u1 + m2u2 = m1V1 + m2V2
0 = 75 * (2 + 7230/48461) - 1000*v2
v2 = 0.161 ms-1
I calculated this with respect to the car. Do I get it right? For this kind of question, what should be taken as the reference, the car or the ground?
ThanksEDIT : I just realized my mistake. The reference should be ground and when person 2, 3 and 4 jump off one by one, there should be initial momentum relative to the ground. I'll amend my calculation in the next post
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