I'm right and the book is wrong

[amar]

I refer to: Question 6b of Chapter 2, in Jacaranda Physics 2

A car of mass 1500 kg travelling due west at a speed of 20 m s-1 on an icy road collides with a truck of mass 2000 kg travelling at the same speed in the opposite direction. The vehicles lock together after impact.

(a) What is the velocity of the tangled wreck immediately after the collision?

(b) Use your answer to part (a) to determine what impulse is applied to the truck during the collision.*

Does the book have an error?



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Instead of: 2.86x2000 - 20x2000

shouldn't we work it out as:

2.86x3500 - 20x2000



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My working out incorporates the new mass of the combined wreck

Why am I wrong?

[Akirus]

Here's what I got.

For the vehicle heading west:









For the vehicle heading east:









Combine the figures after collision.

For the total momentum, perform a vector addition:



The mass is equal to the total of the two vehicles:



Plug it into the momentum equation to find velocity.







Then for b...

The change in momentum of the truck is equal to the impulse, so...




Since it asks for the impulse applied to the truck only, you should only use the mass of the truck in the calculation of , not the mass of the wreck afterwards.

[amar]

since it asks for the impulse applied to the truck only we should only consider the mass of the truck and not the wreck afterwards.

ok.

thanks akirus