## Homework Statement

When you sit on a chair, the resultant force on you is ..?

## The Attempt at a Solution

Down, because of gravity?

## Homework Statement

In the absence of an external force, a moving object will:
stop immediately
slow down and eventually come to a stop MY ANSWER
go faster and faster
move with constant velocity

## Homework Statement

An object is placed on an inclined plane. The angle of the incline is gradually increased until the object begins to slide. The angle at which this occurs is theta. What is the coefficient of static friction between the object and the plane?

## Homework Equations

tan(theta)
That's what I understood, but I need to make sure...

Thanks!

All of your answers are incorrect. Try again, draw force diagrams and really think these problems through.

For the first one, the force on the chair is down, but the force on me is up... Would this be correct?

For the second one, I reviewed the laws, and I would say that the velocity would stay constant (unless some external force came into play). Would this be correct?

berkeman
Mentor
For the first one, the force on the chair is down, but the force on me is up... Would this be correct?

EDIT -- And I believe that your answer for the 3rd one is correct, $$\mu_s = tan( \Theta )$$

Last edited:
Are you absolutely sure my last answer is incorrect?...

The Prenhall website has the same question. I entered an answer other than tan to make sure, and I got:
An object is placed on an inclined plane. The angle of incline is gradually increased until the object begins to slide. The angle at which this occurs is θ. What is the coefficient of static friction between the object and the plane?

sin θ

tan θ

You mean that if F doesn't change, and m doesn't change, a will be constant?

berkeman
Mentor
For the second one, I reviewed the laws, and I would say that the velocity would stay constant (unless some external force came into play). Would this be correct?

That is correct.

berkeman
Mentor
You mean that if F doesn't change, and m doesn't change, a will be constant?

No, I mean that if there is no external force, the acceleration is zero. And you correctly inferred that this means the velocity is constant.

Thank you!

the resultant force on me is mg upward where m is my mass angd is acceleration due to gravity

in absence of external force body moves with constant velocity