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2 trolleys connected to a spring

Question is attached. Kindly show your working. Answer scheme says B
(edited 6 years ago)
Physics question.png109.8KB
Original post by Helping Hand 555
Question is attached.

m1m2 \frac {m1} {m2}
Original post by Anfanny
m1m2 \frac {m1} {m2}


How did you work it out? Answer scheme says B
A or B depending whether you want the ratio v2/v1 or v1/v2

but the velocities will be in opposite directions so the question should have asked about speed really.

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Force from the spring is equal magnitude on both trollies and acts for an equal time so the momentum of trolley a and the momentum of trolly b must sum to zero - it's a conservation of momentum type question.
Original post by Joinedup
but the velocities will be in opposite directions so the question should have asked about speed really.


It did in effect, it asked for 'magnitude of velocities' a.k.a speed. Double reading Qs is a must!
M I see proportional to V
M is not proportional to the root of V
So it can only be A or B
It's like an equation vs an identity
Or a law
Depending on what they said first or second m1 or m2 is a true the top or bottom.
It's really just common sense
Original post by Physics Enemy
It did in effect, it asked for 'magnitude of velocities' a.k.a speed. Double reading Qs is a must!


alright - it's still an ambiguous question tho'
Original post by Physics Enemy
Magnitude of vector = scalar, it was designed to catch people out. Just carefully double read Qs incase.


So why's it definitely B and not A?- that remains the most serious fault in the question after any number of careful readings readings.

question is ambiguous for this reason.
Original post by Joinedup
So why's it definitely B and not A?- that remains the most serious fault in the question after any number of careful readings readings.

question is ambiguous for this reason.


Vectors has nothing to do with it though. The Q introduced masses m1 then m2; if it asks for ratio of speeds, makes sense to calc v1/v2 = m2/m1, Ans b.
(edited 6 years ago)
Original post by Physics Enemy
Vectors has nothing to do with it though. The Q introduced masses m1 then m2; if it asks for ratio of speeds, makes sense to calc v1/v2 = m2/m1, Ans b).


Nope not seeing it tbh
Original post by Physics Enemy
You're comparing object #1 with #2. It's convention to put the first object on top of the fraction and the object being compared with it on the bottom.



No I think I get that but I don't see why #2 goes on top? Surely if I compare "x" with "y" then I want a X:Y, which is the same as saying X/Y=k right?
Original post by DrSebWilkes
No I think I get that but I don't see why #2 goes on top? Surely if I compare "x" with "y" then I want a X:Y, which is the same as saying X/Y=k right?


We're comparing speeds, not masses. I said #1 on top (v1), #2 on bottom (v2), v1/v2 = m2/m1 (from m1v1 = m2v2).
Original post by Physics Enemy
v1/v2 = m2/m1 (from m1v1 = m2v2).


Ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh I see what you meant now.
You see I thought m1 was related to v1 ... ... fair enough

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