Question

I really need help with these questions. My teacher doesn't provide me with anything to go on only some formulas and maybe 3 examples. It would be greatly appreciated!

1. Find the speed of a rock which is thrown off the top of a 20 m tall building at 15 m/s when it makes contact with a bird which is flying at an altitude of 10 m above the ground.

2. A 50 kg roller coaster car is launched, from ground level, at 20 m/s. How fast will it be moving when it reaches the top of a loop, which is 12 m above the ground?

3. A 200 g model rocket is observed to rise 100 m above the ground after launch. What must have been the launch speed of the rocket at the ground?

Answer 1

1.
initial kinetic energy = (1/2)m (225)
went down from 20 meters to 10 meters
potential energy went down by m g h
= m (9.81)(10)
so gain ke of m (9.81)(10)
so now total ke = (225/2) m + 98.1 m
= (1/2) m v^2
so
v^2 = 2 (113+98.1)

2. same as 1 above
ke at bottom = (1/2) m (400)
loses m (9.81)(12)
so
(1/2) v^2 = 200 + 9.81*12

3. LOL, same problem once again, your turn (must have gone straight up)