The discussion revolves around a momentum problem involving Mr. Green, who steps off a boat, and the resulting motion of the boat. The participants explore the principles of momentum conservation in a system where two objects are initially at rest.
The discussion is ongoing, with participants providing hints and guidance regarding the momentum calculations. There is an exploration of different interpretations of the problem, particularly concerning the signs of momentum and the relationship between the velocities of Mr. Green and the boat.
Some participants note the lack of information regarding time or distance, which complicates the calculation of velocity. The discussion also highlights the importance of correctly applying vector principles in momentum calculations.
nonthesecond said:Mr Green, mass 80 kg, stepped off a boat of mass 35 kg at a speed of 3m/s. how fast did the boat move in the opposite direction?
i have no idea how to work it out?
PeterO said:I think you will find that Mr Green and the boat are assumed to be at rest initially, so the total momentum was - and will remain - zero.
PeterO said:I think you will find that Mr Green and the boat are assumed to be at rest initially, so the total momentum was - and will remain - zero.
nonthesecond said:i still don't understand i don't understand what formula to use as well.
PeterO said:If you define the direction Mr Green goes as positive, he will have some positive momentum after he leaves the boat.
To maintain a total of zero, the boat must have an equal sized, but negative momentum - so it will be traveling at an appropriate speed in the negative direction (ie the other way)
nonthesecond said:i think i remeber my teacher saying that it's: 80 + 35= 115
115 x 3 = 375
375/35 = 1.3...m/s
is that correct?
nonthesecond said:i think i remeber my teacher saying that it's: 80 + 35= 115
115 x 3 = 375
375/35 = 1.3...m/s
is that correct?
PeterO said:answer these in order:
What is Mr Green's mass?
What is Mr Green's velocity?
What is Mr Green's momentum?
What is the boat's momentum?
What is the boat's mass?
What is the boat's velocity?
nonthesecond said:you are very kind for helping me.
80kg correct
(+3) - but you didn't answer that question
+240 kg m/s almost correct
105 kg m/s incorrect
35kg correct
no idea for velocity i know formula is f=d/t but you aren't given time or distance.
PeterO said:For that final velocity - think about how you calculated the momentum of Mr Green - and don't forget to use + and - signs correctly.
Velocity is a vector; so can be positive or negative.
EDIT: Hint - answers 3 and 4 add up to zero
PeterO said:For that final velocity - think about how you calculated the momentum of Mr Green - and don't forget to use + and - signs correctly.
Velocity is a vector; so can be positive or negative.
EDIT: Hint - answers 3 and 4 add up to zero
nonthesecond said:is the answer 240/35?