# Magnitude of acceleration of block

How do I find the magnitude of the acceleration of a block along a inclined plane?

I am given the mass of the block = 4.15kg on a no-friction inclined plane of an angle 30 degrees.

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Doc Al
Mentor
What forces act on the block? Find the net force, then apply Newton's 2nd law.

What forces act on the block?

Would that be normal force which is the weight? (40.67? Am I right?)

Newton's 2nd law? F = ma

Can you explain that? How do I find F? m is given as 4.15. Am I right?

Doc Al
Mentor
What forces act on the block?

Would that be normal force which is the weight? (40.67? Am I right?)
The normal force is one of the forces acting on the block, but it does not equal the weight.

The normal force acts perpendicular to the plane; the weight acts down. Draw a diagram and find components of the forces parallel and perpendicular to the plane.

My diagram has the normal force that keeps it up. The weight force pulling it down which opposite of normal force. And tension moving it forward. Am I right?

Doc Al
Mentor
My diagram has the normal force that keeps it up. The weight force pulling it down which opposite of normal force.
No. If the weight were equal and opposite to the normal force, the block would just sit there.
And tension moving it forward.
Tension from what?

The weight force has components parallel and perpendicular to the incline. (What are those components?) The perpendicular component of the weight is equal and opposite to the normal force--so they cancel out. But that leaves the other component of the weight acting down the incline.

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Okay...so I used the m*g*sin30

m = 4.15
g = 9.8

and I still got the wrong answer.

then i divided by mass again and got wrong answer again.

Delphi51
Homework Helper
We need more information to understand what has gone wrong. Show your calcs for normal force, friction force and force along the ramp. Finally, your F=ma calc to find the acceleration.

Doc Al
Mentor
Okay...so I used the m*g*sin30
OK, that's the net force acting on the block.

m = 4.15
g = 9.8

and I still got the wrong answer.