PHYS121 Winter 2000
A few students wrote:

I am unsure even where to begin on problem 2-73 in Resnick Halliday and Krane. Help?

Prof. Seidler responds:

There are probably several ways to solve this problem. Below are the steps for one way to approach it:

1. Let vL denote the initial velocity of the ball as it passes the lower mark. Similarly, let vU denote the intitial velocity of the ball as it passes the upper mark.
2. Determine DtL in terms of vL and g. Similiarly, determine DtU in terms of vU and g.
3. Use equation 20 of chapter 2 to get an expression relating vL to vU in terms of g and H.
4. Use the result of the preceding step to express DtU in terms of g, vL, and H.
5. Verify the desired equation in problem 73 by directly substituting your expressions for DtL and DtU into the expression. The unknown quantity vL will drop out of the expression.