Question

Beatrice throws the 1st calculator straight up from the edge of the roof of a building. She drops a 2nd calculator off the side of the building 2 seconds after she has thrown the first one. If the height of the building is 40m, what must the initial upwards velocity of the 1st calculator be so the two calculators to hit the ground at exactly the same time?

Answer 1

first calc: hf=hi+vi*t-4.9t^2
second calc: hf=hi-4.9(t-2)^2

0=40+vi*t-4.9t^2
0=40-4.9(t-2)^2 well, two equations, two unknowns. start the with the second, solve for time, then put that into the first equation and solve for vi.