# Homework Help: Net Force of farm tractor

1. Dec 1, 2005

### kayteedee

A farm tractor tows a 4300-kg trailer up a 26 Degree incline at a steady speed of 3.0 m/s. What force does the tractor exert on the trailer? (Ignore Friction).

I've tried using 3.0 m/s as the acceleration, because I don't have enough information to derive the acceleration from the kinematics equations. I've tried applying the 26 Degree on either the ma (F=ma) side, both the ma side and the F side, or only the F side, but it won't come out to the answer. (18 kN).

Thank you!

2. Dec 1, 2005

### mezarashi

WRONG!

This is probably the last and worst thing any physics teacher will ever want to hear, the confusion of velocity for acceleration. The units for acceleration are m/s^2. Constant velocity is equivalent to no acceleration. What does this mean? Fnet = 0.

The question is basically asking you, what force is needed to keep a 4300 kg trailer on the 26 degree incline.

3. Dec 1, 2005

### Pengwuino

3m/s is not your acceleration. If there is no acceleration, then there must be no net force. And what force is there going downwards that must be equalized?

4. Dec 1, 2005

### kayteedee

Thanks for the replies, sorry about the acceleration and velocity confusion, I'm just really lost.

If there is no net force, then how would I find the force needed to keep the tractor on a 26 degree incline? I have only learned about Net Force and Newton's Three Laws so far.

5. Dec 1, 2005

### Pengwuino

well at what speed is the trailer being accelerated downwards (and you must compensate for it being on an incline)? Find that and you can determine what speed the tractor must be accelerating upwards to cancel out the downstairs acceleration by gravity.

6. Dec 1, 2005

### kayteedee

Is it accelerating with gravity? Does I need to use the velocity to solve this problem?

7. Dec 1, 2005

### Pengwuino

The velocity has nothing to do with this problem since we're looking for forces. Yes, gravity is accelerating the trailer downwards (but not at 9.8... you must factor in the slope). Think of a ball falling as you drop it out of your hand. Now think of a ball rolling down a 60 degree incline... and then think of it going down a 5 degree incline. The accelerations change as the slope changes.

8. Dec 1, 2005

### kayteedee

So for this problem all I had to do was do 9.8sin26 degrees and multiply that by the mass?

9. Dec 1, 2005

### mezarashi

After a couple more years of physics, yes this problem would be "all I had to do" for you not a sweat. It's relatively trivial. But for the moment, really try to understand what you are doing and the physical principles you are applying ^_^. Oh, and yes, the tension T would be = mgsin26