elementary particle dynamics (1 Viewer)

[marsenal]

I'm having trouble with the questions from the Patel blue book, partly because I don't do Physics but anyway here's one of them:

A smooth block of mass 2kg slides down an incline making an angle of tan^-1(3/4) with the horizontal. Find the acceleration and the magnitude of the normal reaction.

Does the magnitude of the normal reaction mean how far the block travels or what? Thanks.

 

[Affinity]

The normal reaction means the force which the incline plane exerts on the block.




Solution(A little wordy, I don't set work out too well ):

The only forces acting on the block are
1. Gravity of magnitude 2g downwards
2. the Normal reaction force.

The normal reaction force does not contribute to the acceleration because it is perpendicular to the direction of the acceleration.

The force due to gravity could be separated into two components, one perpendicular to the plane and one paralell to the plane.

again, it is only the paralell component which contributes to the acceleration.

this component of the force has magnitude sin(arctan(3/4))*2g
= 3/5 *2g = (6g)/5

a = F/m = 3g/5

the sum of the normal reaction force and the normal component of gravity must equal 0.

The normal component of gravity has magnitude

cos(arctan(3/4))*2g=(4/5)*2g = 8g/5

the normal reaction should have the same magnitude which is (8g)/5

 

[marsenal]

Thanks for such a quick response. I guess I've just got to really think about these questions and draw good diagrams, and obviously do heaps of examples.