Friction of an object being pulled up/down

[Intrusionv2]

Homework Statement

Find the normal force on an object, 80kg, which is being pulled by a force of 4000N. A) Up at an angle of 50 degrees, B) Down at an angle of 70 degrees

Homework Equations

Fn = Fwcosx
Fp = Fwsinx

The Attempt at a Solution

A)
Fp = Fwsinx
Fp = 4000sin50 = 3064N
(80*9.8) - 3064 = -2280N = 2280N

B)
Fp = 4000sin70 = 3758.8N
(80*9.8) + 3758.8 = 4542.7N

Is this correct?

 

[quantumdude]

I'm confused. Is the object being pulled up an inclined plane, or is it on a flat surface and the applied force acts at the given angles?

 

[Intrusionv2]

Pulled up on an inclined plane.

 

[quantumdude]

In that case your "Relevant Equations" are wrong. You need to draw a free body diagram and apply Newton's 2nd law to it. That's how you do every inclined plane problem.

 

[Intrusionv2]

In that case your "Relevant Equations" are wrong. You need to draw a free body diagram and apply Newton's 2nd law to it. That's how you do every inclined plane problem.

Ah...I believe I was doing the other scenario then. In that case, I would simply do Fn = 80 * 9.8 * cos 50 = 503.9 N and Fn = 80 * 9.8 * cos70 = 268.14N, correct?

 

[quantumdude]

The other scenario doesn't make much sense. If you pull on an 80 kg object with 4000 N at 50 degrees, the object will be lifted right off the ground. Hence, no normal force.