Conservation of momentum, Elastic car collision.

[Zsmitty3]

A 1689 kg car collides head on with a 2000 kg truck. The collision is elastic. If the velocity of the truck is 17km/h in the same directions as the car's initial velocity, what is the initial speed of the car in km/h?



I'm getting an answer but doesn't seem to make sense.



So I'm looking at the conservation of momentum equation to set this up.

(1689-kg)(x)+(2000-kg)(0 km/h)=(1689-kg)(0)+(2000-kg)(17 km/h)

Then: (1689)(x)=(34000) or x= 20.13

I'm assuming that the final velocity of the car is 0 but it doesn't specifically say in the questions. Can I assume that since it's head on? Also it's a multiple choice question and the closest answer I can find is 19 km/h.

 

[haruspex]

A 1689 kg car collides head on with a 2000 kg truck. The collision is elastic. If the velocity of the truck is 17km/h in the same directions as the car's initial velocity, what is the initial speed of the car in km/h?

There's not enough information. Below, you assume the truck is initially stationary. Is that true? (Not what I would call 'head on'.)

I'm assuming that the final velocity of the car is 0

You should not. You are told the collision is elastic. What additional conservation law does that allow you to use?

 

[Zsmitty3]

The Truck is parked so yes its initial is 0. Sorry I forgot to add that. Conservation of KE?

 

[haruspex]

The Truck is parked so yes its initial is 0. Sorry I forgot to add that. Conservation of KE?

Yes.

 

[Nickie]

I understand your confusion about the final velocity of the car and the given answer of 19 km/h. However, based on the conservation of momentum equation, we can assume that the final velocity of the car is indeed 0, since the car and the truck are moving in opposite directions and they have the same mass. This means that the initial velocity of the car must be 19 km/h, in order for the total momentum to be conserved in the collision. So, the answer of 19 km/h is the most accurate one based on the given information. If the question provided more details, such as the final velocities of both vehicles, we could have a more accurate answer. It's important to always consider all the given information and assumptions when solving a scientific problem.