# Isaac Physics - Three Collisions Help!! Watch

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Can someone help me with this question?

"Three particles A, B, and C lie at rest in that order in a straight line on a smooth horizontal table. The particle A is then projected directly towards B with velocity uu. Particle A collides with B which then collides with C. Each of the particles has mass mm, and the collisions are elastic.

What is the velocity v1 of particle A immediately after the collision with particle B? Give your answer in terms of u and m."

I know this is really easy but I have no idea where I'm going wrong! m always cancels for me so I can't get it in the right format

"Three particles A, B, and C lie at rest in that order in a straight line on a smooth horizontal table. The particle A is then projected directly towards B with velocity uu. Particle A collides with B which then collides with C. Each of the particles has mass mm, and the collisions are elastic.

What is the velocity v1 of particle A immediately after the collision with particle B? Give your answer in terms of u and m."

I know this is really easy but I have no idea where I'm going wrong! m always cancels for me so I can't get it in the right format

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#2

This is an awfully peculiar result, and one you shouldn't forget.

So you have your three particles lined up on a table, each with initial velocity . Particle is projected towards particle with a velocity . You should draw a diagram now! With a before and after velocity. My diagram looks like this:

Now then, let's do the maths. We remember that momentum is conserved in all collisions: therefore, the net momentum before the collision is equal to the net momentum after.

Therefore

.

For a perfectly elastic collision, kinetic energy is also conserved:

.

Solving simultaneously for (the desired velocity) we get

. So the velocity of after the collision is 0.

So you have your three particles lined up on a table, each with initial velocity . Particle is projected towards particle with a velocity . You should draw a diagram now! With a before and after velocity. My diagram looks like this:

Now then, let's do the maths. We remember that momentum is conserved in all collisions: therefore, the net momentum before the collision is equal to the net momentum after.

Therefore

.

For a perfectly elastic collision, kinetic energy is also conserved:

.

Solving simultaneously for (the desired velocity) we get

. So the velocity of after the collision is 0.

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#3

(Original post by

Can someone help me with this question?

"Three particles A, B, and C lie at rest in that order in a straight line on a smooth horizontal table. The particle A is then projected directly towards B with velocity uu. Particle A collides with B which then collides with C. Each of the particles has mass mm, and the collisions are elastic.

What is the velocity v1 of particle A immediately after the collision with particle B? Give your answer in terms of u and m."

I know this is really easy but I have no idea where I'm going wrong! m always cancels for me so I can't get it in the right format

**Satsuko**)Can someone help me with this question?

"Three particles A, B, and C lie at rest in that order in a straight line on a smooth horizontal table. The particle A is then projected directly towards B with velocity uu. Particle A collides with B which then collides with C. Each of the particles has mass mm, and the collisions are elastic.

What is the velocity v1 of particle A immediately after the collision with particle B? Give your answer in terms of u and m."

I know this is really easy but I have no idea where I'm going wrong! m always cancels for me so I can't get it in the right format

0.5mu² = 0.5mv1² + 0.5mv2² => u² = v1² + v2²

So v2 = u - v1, v2 = √(u² - v1²)

Equate and solve for v1, only keep feasible solution.

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#4

Has anyone actually got an answer for this? I keep struggling and am having the same problem with getting the answer into the correct format, always end up with v2 in the equation which i cant get rid of

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#5

(Original post by

Has anyone actually got an answer for this? I keep struggling and am having the same problem with getting the answer into the correct format, always end up with v2 in the equation which i cant get rid of

**reecesmith**)Has anyone actually got an answer for this? I keep struggling and am having the same problem with getting the answer into the correct format, always end up with v2 in the equation which i cant get rid of

Use conservation of kinetic energy

Thus relative speed of approach = relative speed of separation

Use conservation of momentum

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#6

(Original post by

Post 2 explained that the answer is 0

Use conservation of kinetic energy

Thus relative speed of approach = relative speed of separation

Use conservation of momentum

**BobbJo**)Post 2 explained that the answer is 0

Use conservation of kinetic energy

Thus relative speed of approach = relative speed of separation

Use conservation of momentum

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#7

(Original post by

yh i also came to an answer of 0 which I understand but even using the steps that your saying I just cant get it into the correct form

**reecesmith**)yh i also came to an answer of 0 which I understand but even using the steps that your saying I just cant get it into the correct form

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#8

(Original post by

What do you mean? What correct form? The answer is 0

**BobbJo**)What do you mean? What correct form? The answer is 0

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#9

(Original post by

its on isaac physics and it wants v1 ( the velocity of ball A after impact) in terms of m(mass of ball) and u( its initial velocity)

**reecesmith**)its on isaac physics and it wants v1 ( the velocity of ball A after impact) in terms of m(mass of ball) and u( its initial velocity)

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#11

(Original post by

I don't think it lets you

**reecesmith**)I don't think it lets you

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#12

(Original post by

did you try? can you give the link to the question

**BobbJo**)did you try? can you give the link to the question

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#13

(Original post by

did you try? can you give the link to the question

**BobbJo**)did you try? can you give the link to the question

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#14

(Original post by

srry the link is taking ages it keeps saying they need to verify the message just type in isaac physics and under a momentum and collisions section there should be a question called three collisions

**reecesmith**)srry the link is taking ages it keeps saying they need to verify the message just type in isaac physics and under a momentum and collisions section there should be a question called three collisions

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#15

(Original post by

wth im getting scammed i put that

**BobbJo**)I put 0 and it said correctwth im getting scammed i put that

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#16

(Original post by

(Original post by

wth im getting scammed i put that

**reecesmith**)(Original post by

**BobbJo**)I put 0 and it said correctwth im getting scammed i put that

you should have tried 0

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#18

(Original post by

i did that in the first place idk why that didnt work, sorry bout that

**reecesmith**)i did that in the first place idk why that didnt work, sorry bout that

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