The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

M4 (Logic problem)

In Ex2B Q. 14, sphere A initially has a velocity 2i+5j and sphere B has 2i-2j, after collision sphere A has velocity 3i+4j.
But when I tried to calculate the coefficient of restitution, I found that using (Vb-Va)/(Ua-Ub)=e would get me a negative answer, and then I realized this would be physically impossible, as A would have to go through B to have a velocity of 3i+4j.
Sorry there isn't a question here, it's just that this question is bothering me.
Original post by simonli2575
In Ex2B Q. 14, sphere A initially has a velocity 2i+5j and sphere B has 2i-2j, after collision sphere A has velocity 3i+4j.
But when I tried to calculate the coefficient of restitution, I found that using (Vb-Va)/(Ua-Ub)=e would get me a negative answer, and then I realized this would be physically impossible, as A would have to go through B to have a velocity of 3i+4j.
Sorry there isn't a question here, it's just that this question is bothering me.

Hey, I only do M2 and M3 but this is relevant to what I've done thankfully. From looking at the velocity vectors, you have A coming in from the south towards the north, with the same horizontal component of velocity as B, only B is moving north to south and slower in the j-axis.

The final velocity vector of A shows that it continues to move north, simply at a slower speed (which is logically what you would expect), and you would then assume that the direction of B in the j-axis is reversed (from negative j value to positive).

So to get the final speed of B, use COLM (Conservation of Linear Momentum).

And for NLR, (Newton's Law of Restitution) if you say -e = u1-v2/u+v, taking north as positive.

Not seen a problem exactly like this in M2/M3 (Edexcel) but I gave it my best shot.

Hope this helps :smile:
Reply 2
Avatar for Phichi
Phichi
11
Original post by simonli2575
In Ex2B Q. 14, sphere A initially has a velocity 2i+5j and sphere B has 2i-2j, after collision sphere A has velocity 3i+4j.
But when I tried to calculate the coefficient of restitution, I found that using (Vb-Va)/(Ua-Ub)=e would get me a negative answer, and then I realized this would be physically impossible, as A would have to go through B to have a velocity of 3i+4j.
Sorry there isn't a question here, it's just that this question is bothering me.


State Newtons Law of Restitution in words. Apply it to the problem.

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you