# Homework Help: Question about interacting objects

1. Jul 6, 2010

### sona1177

A 1000 kg car pushes a 2000 kg truck that has a dead battery. When the driver steps on the accelerator, the drive wheels of the car push backward against the ground with a force of 4500 N.

A) what is the magnitude of the force of the car on the truck?

B) what is the magnitude of the force of the truck on the car

Before I start, I just want to make sure if I use static friction and not kinetic friction, right since tires are just rolling and not sliding?

2. Jul 6, 2010

### ehild

Use static friction. It is bad if the wheels slide at start.

ehild

3. Jul 6, 2010

### sona1177

I got 3000 N for both by using static friction as the friction component and drawing the force of the wheels as pointing to the right for the Free Diagram of the car. Are these assumptions that I have made valid?

4. Jul 6, 2010

### Staff: Mentor

Yes and your answers are correct. (It is most likely static friction at work--at least one hopes so. But it really doesn't matter for this problem, since you are told what the force is that the tires exert against the ground.)

5. Jul 6, 2010

### sona1177

Great! Thank you so much for taking the time to help me!