Answer:
a) Both balls are affected by gravity in the same way. The time both balls hit each other is equal to the time the ball thrown up reaches the top of the roof, if there was no gravity. (both balls would be at the same location)
y = v*t = 85m = 46m/s * t
t = 1.85s
Check:
The equation for position is given by:
y(t) = -0.5gt² + v₀t + x₀
The position of the ball on the roof top at time t = 1.85s:
y₁(t) = -4.9t² + 85.0 = 68.3m
The position of the ball thrown up at time t = 1.85s:
y₂(t) = -4.9t² + 46 * 1.85 = 68.3m
b) the two balls hit each other at a hight of 68.3m
