# Homework Help: [Physical Science] Force

1. Jan 25, 2005

### Jessi

I was just hoping someone could check the work I did on this two part problem? :)

18a. A car has a mass of 1200 kg. What's the weight of the car?

Answer: 1200 kg*9.8 m/s^2 = 11760 N.

b. Disregarding friction, what force must the car motor apply to accelerate the car along a level highway at the rate of 4.0 m/s^2?

Answer: 11760 N/4.0 m/s^2 = 2940 kg.

Last edited: Jan 25, 2005
2. Jan 25, 2005

### Staff: Mentor

Right!

No. You need to use F = ma. (Note that force must have the units of force, which is N. Mass (measured in kg) is not a force.)

3. Jan 25, 2005

### Jessi

Oh, okay! :) Thank you for helping me.

So is it 11760 N*4.0 m/s^2 = 47040? I don't understand what the unit is, though - I thought I'd already used N in the problem, so it had to be mass. Does that not matter?

4. Jan 25, 2005

### Staff: Mentor

No! This problem has nothing to do with the weight of the car.

Use F = ma, which means:
Force needed to accelerate car = (mass of car) x (acceleration).

The answer will be in N, the unit of force.

5. Jan 25, 2005

### Jessi

Alrighty!

1200 kg (mass of car)*4.0 m/s^2 (acceleration) = 4800 N?

*hopeful*

6. Jan 25, 2005

### Gokul43201

Staff Emeritus
Yes, that's right.

7. Jan 25, 2005

### Jessi

Wonderful! Thanks, both of you.