A ruler is attached to a tree, 1.27m up the ground. An acorn falls from the tree, if it took 0.196s to pass the ruler, how high was it before it fell?

Question

Assume the acorn didn't hit anything as it fell.

I used the formula: S=ut + 1/2 at^2 to find u. Then I used h=u^2/2a to get h and I added it to 1.27m but my answer was wrong.

Answer 1

I assume you are saying that the ruler is attached 1.27 meters up from the ground. How long is the ruler? The length of the ruler is the S that you need to substitute for to solve for u in your equation( with a = g and the time given). The second equation is also correct for solving for the height from rest that will result in the velocity, u. Finally, you are correct to add the 1.27m at the end to get the height up the tree.

There is a similar problem involving someone timing a pot fall past a window and determining how high up above the window the pot is released. (you have to know the size of the window.