# Homework Help: Net Force Exerted On A Object?

1. Dec 18, 2007

### cpuboye11

Hi,

I would like to first open this post by saying that I am not a slacker, and I try my hardest to figure things out to the best of my abilities.

I am in Physics 1 right now. We are studying what our book calls Forces in One Dimension.
I have a problem, the problem being I have a chapter test tomorrow and no hope of passing.

One of the problems that seem to hunt me and can't figure out for the life of me is finding out the net force that is exerted on a object; such as this:

A race car has a mass of 710 kg. It starts from rest and travels 40.0 m in 3 secs. The car is uniformly accelerated during the entire time. What net force is exerted on it?

It seem it is a easy problem for most people in Physics but I just can't figure it out. Little help please?

Thanks Kyle

2. Dec 18, 2007

### arildno

Determine the acceleration by means of 3 pieces of information given:

1. The acceleration is uniform, i.e, equal to some constant "a"
2. Its initial velocity is zero
3. It travelled 40 meters in 3 seconds.

Set up the relevant kinematic equation, and solve for "a"

Then find the net force exerted upon the car at any given moment by means of Newton's 2.law of motion.

3. Dec 18, 2007

### cpuboye11

*Sorry for putting the topic in the wrong spot*

So this is what i understand or it seems,

Vi = 0
Vf = 40**********
a = ?
t = 3
So i did this: 40-0 / 3 = 13.33

Now, maybe I am just being dumb; but don't I just * 13.33 by the Kg's which is 710kg?

And get 9464?

4. Dec 19, 2007

### arildno

It is not the final velocity that equals 40, don't mix up distance and velocity!!

We have that, since the initial velocity is 0, the distance s travelled in t seconds under uniform acceleration "a" is given by:
$$s=\frac{a}{2}t^{2}$$
Now, solve for "a", knowing that s=40, t=3.

5. Nov 13, 2009

### mause82

hi i have a problem and i need you help...
2.0 kg mud ball drops from rest at height ok 15m. If the impact between the ball and the ground lasts 0.50s. what is the average net force exerted by the ball on the ground.
this is the problem. can you help me