# Homework Help: Newton's law application

1. Mar 23, 2004

### nutzweb

hey guys! i need some help, a big help. this is urgent... can somebodyhelp me solve this problem:

what force, applied parallel to the plane, is necessary to move a 16 kg object up africtionless palne with a uniform acceleration of 2.0 m/s2 if the plane makes an angle of 60 degrees with the horizontal?

pls somebody help me. i really need it badly. hope somebody would reply today. thanks...

2. Mar 23, 2004

### outandbeyond2004

Is the plane on the surface of earth, so that the body is subject to a gravitational force of (16 kg)*(9.8 m/s^2)?

Is the acceleration wrt the plane or the ground? Makes a big difference.

I assume the answers are yes and wrt the plane.

The NET force necessary to move the body 2 m/s^2 is simply mass * acceleration = (16 kg)*(2 m/s^2).

However, you need more than that to overcome the gravitational force. The body is kept from moving straight down by the plane, so it would only go down the plane with a force of (16 kg)*(9.8 m/s^2)cos 30 degrees. Reverse that force and add to the above ("NET").

Now, I may have made a mistake somewhere, so go over that solution carefully. Don't blame me, it was a rush job, right, boss?

3. Mar 26, 2004

### Staff: Mentor

The component of the object's weight parallel to the plane is $mg\sin\theta$ acting down the plane. The applied force F (acting up the plane) must be enough to overcome that and produce the needed acceleration:
$$F = mg\sin\theta + ma$$