Q. A block of mass 3kg travelling at 5ms-1 catches up another block of mass 7kg travelling at 2ms-1 along the same line and in the same direction.
a) If after the collision the second block has increased its speed to 3ms-1, what is the speed of the first block?
b) You are given that the difference between the speeds of the two blocks after the collision cannot be greater than the difference of the speeds before the collision. Deduce that the speed, v ms-1, of the first block after the collision must satisfy the inequalities 0.8 <=v<=2.9.
I have done a) - just a simple standard momentum question - but how do I go about doing part b) ...?
If given that the difference in speeds of the two blocks cannot be greater than that of the two blocks before the collision then we can generate the inequality that:
mod(V(2)-V(1)) <= 3 but I am not sure if this helps at all. Can someone help?..
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Mathematicus65
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- 19-02-2016 15:07
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Mathematicus65
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- 19-02-2016 18:17
anyone...?
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- 19-02-2016 18:22
(Original post by Mathematicus65)
anyone...?
I'm heading out now, and haven't had a chance to find the upper bound, hopefully that'll get you started. -
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- 19-02-2016 18:24
For A i got a result of 8/3 which is roughly 2.6
so difference before>difference after
5-2=3 and 3-(8/3)=0.3 roughly
so far putting that together i get this 0.3≤v≤3
but i'm not sure how to reach that inequality they've given -
pineneedles
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- 19-02-2016 18:32
I got the lower bound, attached my working if that helps. I basically wrote an equation for the velocity of V2 using conservation of momentum and subbed that ijnto your inequality
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- 19-02-2016 18:34
(Original post by pineneedles)
I got the lower bound, attached my working if that helps. I basically wrote an equation for the velocity of V2 using conservation of momentum and subbed that ijnto your inequality
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- 19-02-2016 18:37
(Original post by thefatone)
where's your working? xD
Here it is, i did ot in a rush and im tired so i may have buggered aomething up
Um, in hindsight, this isnt very helpful as I did some of the steps in my head.Last edited by pineneedles; 19-02-2016 at 18:42. -
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- 19-02-2016 18:47
(Original post by pineneedles)
Lol, im using a tablet and struggling a bit
Here it is, i did ot in a rush and im tired so i may have buggered aomething up
Um, in hindsight, this isnt very helpful as I did some of the steps in my head. -
pineneedles
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- 19-02-2016 18:53
(Original post by drandy76)
i think you use this working, but consider when the other blocks speed becomes 0?
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- 19-02-2016 18:59
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