Newtons Laws

1. Mar 4, 2007

CallingAllCars7

1. The problem statement, all variables and given/known data

A chair of mass 13.0 is sitting on the horizontal floor; the floor is not frictionless. You push on the chair with a force = 45.0 that is directed at an angle of 40.0 below the horizontal and the chair slides along the floor.

[b]2. Relevant equations[/B]

These were given to me to help.
N= w-F1sin()
Fcos()=ma

3. The attempt at a solution

with the equations given to me by the TA I thought that the answer would be 9.8*13-45sin(), but I keep getting the answer incorrect(my class uses masteringphysics for hw) and I even tried all sorts of other crazy equations.

2. Mar 4, 2007

denverdoc

cant let that happen. first of all do you know what is menat by a normal force?

The way i think about it is in terms of sum(forces)=m*a If our object of mass m (chair) is not falling thru the floor, there must be an equal and opposite force acting to prevent it. So sum up all the downward forces, subtract any present that might be lifting the chair, and you have normal force, only its directed upward. In this case the angle is below vertical so any "push" adds to the weight. That help at all?

PS: Also add the questions to the problem as they were omitted on the original post.