Got Homework?
Connect with other students for help. It's a free community.
Here's the question you clicked on:
 0 viewing
pratu043
Group Title
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?
 2 years ago
 2 years ago
pratu043 Group Title
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?
 2 years ago
 2 years ago

This Question is Closed

Xishem Group TitleBest 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.
 2 years ago

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

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

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

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

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

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

Xishem Group TitleBest ResponseYou've already chosen the best response.1
Momenta are vectors.
 2 years ago

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

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

pratu043 Group TitleBest ResponseYou've already chosen the best response.0
even if they are different?
 2 years ago

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

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

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

Xishem Group TitleBest ResponseYou've already chosen the best response.1
The magnitudes aren't different.
 2 years ago

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

Xishem Group TitleBest 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.
 2 years ago

pratu043 Group TitleBest 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?
 2 years ago

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

pratu043 Group TitleBest ResponseYou've already chosen the best response.0
What is a closed system?
 2 years ago

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

Xishem Group TitleBest 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.
 2 years ago

Xishem Group TitleBest 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).
 2 years ago

pratu043 Group TitleBest ResponseYou've already chosen the best response.0
Thanks I got it now.
 2 years ago

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

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

Xishem Group TitleBest 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.
 2 years ago
See more questions >>>
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.