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One question in EK1001 physics shows a box on an inclined plane with mass of 2 kg at an angle of 30 degrees to the horizontal. The height of the box is 5 m, and the plane has some distance d. It asks for how long it takes to move the distance d.

delta y = 0.5a (delta t)^2
delta y is 10 m because I used xsin30= 5

Then I used mgsin30 for the acceleration of the box down the plane, and I ended up with an answer of t = square root of 2. However, in the book, it says the answer is 2 s.

It appears that they did the same thing as me, except for the acceleration of the box, they used gsin30 and did not include the mass of the box for some reason.

Why is m not included?

Oh nevermind. I forgot that mgsin theta is the force component, and not the acceleration. So you have to set it as a=fnet/m and m cancels.....
 
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