# Homework Help: Center of Mass and car inertia

1. Apr 13, 2014

### Kavorka

I got one multiple choice on our exam incorrect, and I was wondering exactly why this answer is correct:

When you accelerate your car, the front of the car lifts up slightly. Or when you brake, the front dips down. The primary reason is because the
A) center of mass of the car and its contents is below the center of the wheel.
B) center of mass of the car and its contents is above the center of the wheel.
C) center of mass of the car and its contents is at the center of the wheel.
D) center of mass of the car and its contents is above the road.
E) car has inertia.

E is a bit of a default answer because it can be explained by inertia, and that's what I said. A and C can be ruled out. I was pondering B and D far too long which is why I defaulted to E, but the correct answer is D. Why is this?

2. Apr 13, 2014

### SammyS

Staff Emeritus
Where is the force which changes the car's velocity applied ?

3. Apr 13, 2014

### Kavorka

Along the surface of the road?

4. Apr 13, 2014

### SammyS

Staff Emeritus
Yes.

5. Apr 14, 2014

### Kavorka

How does that result in the lifting or dipping of the front of the car when there is acceleration

6. Apr 14, 2014

### SammyS

Staff Emeritus
What do you know about torque?

7. Apr 14, 2014

### Kavorka

It would be acting in the direction of the wheel's axis.