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View Full Version : How far does a block go up a frictionless ramp?


Talby
Oct18-04, 08:11 PM
A block is given an initial velocity of 3.00 m/s up a frictionless 22.0° incline. How far up the incline does the block slide before coming (momentarily) to rest? So basically, how far does it go up before the block starts falling.
http://img11.paintedover.com/uploads/11/p522.gif

At first glance, this seemed really simple to me. Here's what I tried:

The initial velocity in the Y direction would be 3sin(22) = 1.12 m/s

Then I used the formula
Vf2 = Vi2 + 2*(-9.8)*(delta Y)
-->0 = 1.26 - 19.6(delta Y)
so delta Y = .064 m.

But that is straight up, and I need it along the incline. So, I did

sin(22) = (.064)/x
and x gives me .17 as the distance up the incline.

However, neither .064m or .17m is correct. Can anyone tell me what I'm doing wrong? Am I totally off, or just missing a decimal or something?

Doc Al
Oct18-04, 08:29 PM
Use that same kinematic equation (v_f^2 = v_i^2 + 2ax) but use the components along the incline. Hint: Figure out the component of the acceleration due to gravity along the incline.

garytse86
Oct19-04, 01:33 PM
surely you can do it by energy considerations - you know the KE at the start, and no GPE, then at the top there will be no KE momentarily, so you can work out h?