# Homework Help: Mechanics car problem

1. Jun 3, 2010

### TheAntithesis

1. The problem statement, all variables and given/known data
A 1000kg car pushes a 2000kg truck which has a dead battery. When the car driver pushes on the accelerator, the drive wheels of the car push back against the ground with a force of 4500N. Rolling friction can be ignored.
What is the magnitude of the force of the car on the truck?
What is the magnitude of the force of the truck on the car?

Relevant equations
I'm guessing F=ma

The attempt at the solution
I know that the two questions should have the same answer because of Newton's third law, I'm just having a problem setting up the equations. If someone could provide a free-body diagram, that would help a lot.
I've calculated the normal and weight forces for both the car and the truck, 9800N and 19600N respectively. What I don't really understand is the push against the ground of 4500N.

Last edited: Jun 3, 2010
2. Jun 3, 2010

### PhanthomJay

The car's drive wheels push back against the ground with a force of 4500 N, due to friction between the tires and ground. Using Newton 3, with what force and direction does the ground push on the car? That's the force acting on the car-truck system, which accelerates the car and truck together per Newton 2. What is that acceleration of the car and truck together? What's the acceleration of the truck? What force must act on the truck by the car to produce that truck's acceleration?