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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 ms-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?

  • Instead of: 2.86 x 2000 - 20 x 2000
  • Shouldn't we work it out as: 2.86 x 3500 - 20 x 2000

My working out incorporates the new mass of the combined wreck.

Why am I wrong?

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1 
 Hey Gollum, thanks for providing the question, this makes it easier for people to answer it, especially the Uni people who use this site and do not have the book. I deleted your other post to allow clarity, and posted the question you provided HERE. – asa.hoshi Jan 4 at 9:57

1 Answer

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Impulse is defined as the change in momentum.

Hence, the impulse on the truck is defined as the change in momentum on the truck.

So Δp = mΔv = 2000 x (2.86 - 20) = -34280, which is what the book also did!

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