# Friction-less wedge physics problem

1. Sep 26, 2004

### holyko

A 2.0-kg body rests on a frictionless wedge that has an inclination of 65.0° and an acceleration a to the right such that the mass remains stationary relative to the wedge. Find a

This is one of the question i had to do for HW.
Not really asking for an answer but it would be great if you provide one with a semi detail equation

I just don't get how is a body at rest yet accelerating!! I probably misinterpret the question and I hope someone will point out where I misunderstood. Thank You

Last edited: Sep 26, 2004
2. Sep 26, 2004

### Sirus

What they mean is that the wedge with the mass on it is being acclerated (along the floor, for example) in a way that the mass does not slide down the wedge as it would if it were stationary. Try using some basic principles. Very interesting problem.

3. Sep 26, 2004

### holyko

Thx for pointing out my misinterpertation ^_^. Now, the question made more sense.

Ok, I tried doing the question but I got the wrong answer and this is what I did:

I thought maybe mass doesn't matter in this situation cuz all object has the same accelartion due to gravity
so i just went acelaration to the right = 9.8 x sin 65 x sin 25

The sin 65 was to find the accelartion for the body sliding down the incline
this accleration is parallel to the incline

Then i did a bit of geometry to figure out that sin 25 will give me "a" to the right.

so, was i wrong about ignoring the mass or what?

4. Sep 26, 2004

### Pyrrhus

5. Sep 27, 2004

### Staff: Mentor

I'm afraid so.
In any problem concerning acceleration or force, you'd better consider the mass.

Think this way. There are two forces acting on the body: (1) the normal force from the wedge, and (2) the weight. Hint: in the vertical direction, the body does not accelerate; in the horizontal direction, it does. Apply $\vec{F_{net}} = m \vec{a}$.