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pratu043
 3 years 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?
pratu043
 3 years 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?

This Question is Closed

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

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

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0but even in recoiling of gun, how can the final momentum be 0?

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

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0Yes, I know the answer but I can't understand how total momentum is 0.

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

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

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1If you have two vectors in opposite directions, they can cancel eachother out.

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

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0even if they are different?

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1The girl's momentum is in one direction and the boat's in another direction.

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

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0I mean do they cancel each other even if the magnitudes are different?

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1The magnitudes aren't different.

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1Remember, momentum is a function of both mass and velocity.

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1If 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.

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0So mass*velocity of the bullet or girl will always be equal to mass*velocity of gun or boat?

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1Yes, assuming you are in a closed system. Which you are.

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0What is a closed system?

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0Please help I have a test coming up soon.

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1A 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.

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1It 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).

pratu043
 3 years ago
Best ResponseYou've already chosen the best response.0This doesn't happen in the case of a collision right?

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1Momentum is not conserved in an inelastic collision. Momentum is conserved in an elastic collision.

Xishem
 3 years ago
Best ResponseYou've already chosen the best response.1In 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.
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