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Physics - Momentum Question

A bit stuck on a question i need to do for homework, it looks easy enough but i havent got a clue!

- In a laboratory experiment to measure the mass of Object X, two identical trolleys A and B, each of mass 0.50kg, were initially stationary on a track. Object X was fixed to trolley A. When a trigger was pressed the two trolleys moved apart in opposite directions at speeds of 0.30ms-1 and 0.25ms-1 .
a) Which of the two speeds given was for trolley A, give a reason for your answer.
b) Show that X has a mass of 0.10kg

None of the calculations i've tried give the mass of X to be 0.10kg :confused:

0.3m/s-1<---[ A ][X].....[ B ]--->0.25m/s-1

Reply 1

apocalipse117

12

this may be because your speeds for A and B are the wrong way round

Reply 2

2^1/2

11

momentum = mass x velocity

you see that A will be travelling slower as it has more mass, so has the same momentum as B (which has less mass), when travelling slower.

so to work out X

the momentum of A and B must be the same, you know v (for A and B) and you know the mass of B.

can you set-up the eqn?

Reply 3

Cookie29

OP

2

Wow thanks for the quick reply.
Ohhh i see, is that because A + X together is heavier than B so it would move off slower?

Reply 4

Cookie29

OP

2

Thanks very much, 2^1/2.

Reply 5

2^1/2

11

Cookie29

Wow thanks for the quick reply.
Ohhh i see, is that because A + X together is heavier than B so it would move off slower?

exactly, as A has the same momentum when going slower, due to it's larger mass

Reply 6

username3477548

20

hmm im a bit confused with this question too...
using the equation MaVa = - MaVb
you get 0.6 = -(0.5 +x)
x= 1.1 Kg...
the answer is 0.1

i feel like I've messed up with the signs somewhere.... :/

Reply 7

A Smart Guy

2

Can someone show the actual calculation for part b because I'm stuck.
if m = the mass of trolley A + object X:
0.25m = -(0.5 x 0.3) ---> m=-0.6 but mass cannot be negative???

Reply 8

Jozefb

2

If the trolley was 0.5 then plus 0.1 = 0.6 which you got

Original post by Jozefb

If the trolley was 0.5 then plus 0.1 = 0.6 which you got

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Physics - Momentum Question

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