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I have a doubt in the answer key to the problem on law of conservation of momentum.
The question: A girl of mass 50 kg jumps out of a rowing boat of mass 300 kg on to the bank with a horizontal velocity of 3 m/s. With what velocity does the boat move backwards?
Answer key says:
m1(mass of girl) = 50 kg
m2(mass of boat) = 300kg
v1(velocity of girl) = 3 m/s
v2 = ?
m1v1 + m2v2 = 0
How can the momentum of the whole system after the girl jumps out of the boat be 0? The boat will have some momentum right?
 one year ago
 one year ago
I have a doubt in the answer key to the problem on law of conservation of momentum. The question: A girl of mass 50 kg jumps out of a rowing boat of mass 300 kg on to the bank with a horizontal velocity of 3 m/s. With what velocity does the boat move backwards? Answer key says: m1(mass of girl) = 50 kg m2(mass of boat) = 300kg v1(velocity of girl) = 3 m/s v2 = ? m1v1 + m2v2 = 0 How can the momentum of the whole system after the girl jumps out of the boat be 0? The boat will have some momentum right?
 one year ago
 one year ago

This Question is Closed

XishemBest ResponseYou've already chosen the best response.1
Right. The boat must have some change in velocity, since the momentum must be conserved and the momentum of the girl changed.
 one year ago

Yahoo!Best ResponseYou've already chosen the best response.0
it is just same as recoil velocity of Gun..
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
but even in recoiling of gun, how can the final momentum be 0?
 one year ago

Yahoo!Best ResponseYou've already chosen the best response.0
v =  Mv/m = 50*3/300 = 0.5m/s
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
Yes, I know the answer but I can't understand how total momentum is 0.
 one year ago

Yahoo!Best ResponseYou've already chosen the best response.0
Law of conservation of momentum..says that momentum is conserved
 one year ago

Yahoo!Best ResponseYou've already chosen the best response.0
Do..u knw abt Rocket propulsion
 one year ago

XishemBest ResponseYou've already chosen the best response.1
If you have two vectors in opposite directions, they can cancel eachother out.
 one year ago

Yahoo!Best ResponseYou've already chosen the best response.0
even though the mass gets reduced..the momentum is conserved
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
even if they are different?
 one year ago

XishemBest ResponseYou've already chosen the best response.1
The girl's momentum is in one direction and the boat's in another direction.
 one year ago

Yahoo!Best ResponseYou've already chosen the best response.0
yup..@Xishem has a point there
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
I mean do they cancel each other even if the magnitudes are different?
 one year ago

XishemBest ResponseYou've already chosen the best response.1
The magnitudes aren't different.
 one year ago

XishemBest ResponseYou've already chosen the best response.1
Remember, momentum is a function of both mass and velocity.
 one year ago

XishemBest ResponseYou've already chosen the best response.1
If one object with 1kg mass and 10m/s velocity is moving right and another of 10kg mass and 1m/s velocity is moving left, the total momentum is zero.
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
So mass*velocity of the bullet or girl will always be equal to mass*velocity of gun or boat?
 one year ago

XishemBest ResponseYou've already chosen the best response.1
Yes, assuming you are in a closed system. Which you are.
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
What is a closed system?
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
Please help I have a test coming up soon.
 one year ago

XishemBest ResponseYou've already chosen the best response.1
A closed system is a physical system which doesn't exchange any matter in or out of itself and which isn't affected by outside forces.
 one year ago

XishemBest ResponseYou've already chosen the best response.1
It basically just means that you are only considering the two objects and not nonconservative forces like friction which would change the overall momentum. (This case is frictionless, but that's one case where momentum won't be conserved).
 one year ago

pratu043Best ResponseYou've already chosen the best response.0
This doesn't happen in the case of a collision right?
 one year ago

XishemBest ResponseYou've already chosen the best response.1
Momentum is not conserved in an inelastic collision. Momentum is conserved in an elastic collision.
 one year ago

XishemBest ResponseYou've already chosen the best response.1
In the real world, momentum is never conserved in collisions. When two pool balls hit eachother for instance, they release some sound upon impact  this is lost energy. They are also always under the effect of friction from the table.
 one year ago
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