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impule and momentum further maths help

Picture: https://imgur.com/gallery/xBlTy

I have drawn the diagram as stated, but i cant seem to get 15.4m/s for the speed of car B after the collision.

using the formula: speed of separation = e x speed of approach i still cant get close. for Va i get 0.8 x 15 which is 12 and for Vb i get 0.8 x 10 which is 8. i dont understand how to find a faster speed without this formula.

When using mu=mv, i get 1200Va + 800Vb = 26000. if i sub 15.4m/s for the speed of Vb (which i dont know how to get) i get Va = 20.6 m/s. i dont know if thats right becuase surely if a car collides head on with another car, its speed isnt going to increase.

please help me out as im really stuck.

thank you
(edited 6 years ago)
Attachement not found :frown:
Reply 2
Avatar for amin11234
amin11234
OP
10
Original post by Radioactivedecay
Attachement not found :frown:


Ive added the link to my previous post. Ive got it here as well. Thanks for your help.

https://imgur.com/gallery/xBlTy
Original post by amin11234
Ive added the link to my previous post. Ive got it here as well. Thanks for your help.

https://imgur.com/gallery/xBlTy


After the collision, B must move faster than A so
speed of separation = e x speed of approach
becomes Vb - Va = 0.8 x 5
where 5 is the difference in their speeds before the collision.
Now solve the simultaneous equations
Reply 4
Avatar for amin11234
amin11234
OP
10
Original post by tiny hobbit
After the collision, B must move faster than A so
speed of separation = e x speed of approach
becomes Vb - Va = 0.8 x 5
where 5 is the difference in their speeds before the collision.
Now solve the simultaneous equations


Got it, thank you.
Reply 5
Avatar for amin11234
amin11234
OP
10
Original post by tiny hobbit
After the collision, B must move faster than A so
speed of separation = e x speed of approach
becomes Vb - Va = 0.8 x 5
where 5 is the difference in their speeds before the collision.
Now solve the simultaneous equations


I need help with this question as well. i only need part (ii) but i attached part (i) as well.
https://imgur.com/a/JPPx0.

this is my working out for it which gives the wrong answer ive attached my working for part (i) also.
https://imgur.com/95z2STk

i dont know what to do, i feel like ive made a silly mistake somewhere but i just dont know where ive gone wrong.

if you could help me out that would be wonderful.

thank you
(edited 6 years ago)
Original post by amin11234
I need help with this question as well. i only need part (ii) but i attached part (i) as well.
https://imgur.com/a/JPPx0.

this is my working out for it which gives the wrong answer ive attached my working for part (i) also.
https://imgur.com/95z2STk

i dont know what to do, i feel like ive made a silly mistake somewhere but i just dont know where ive gone wrong.

if you could help me out that would be wonderful.

thank you


The error is in part (i). The impulse on B is in the negative direction i.e. towards A, so the equation should be -1100 = 200Vb -4000. At present in part (i) the total momentum has increased, not stayed the same.
Your equations in part (ii) look OK so it should work out with the new version of Vb

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