# A ball is dropped from the roof of a building. How fast is it moving after 4.9 seconds? (Absolute value) [closed]

i really need help. A ball is dropped from the roof of a building. How fast is it moving after 4.9 seconds? (Absolute value) in m/s

A water balloon is thrown downward from a tall building with an initial velocity of 12.9 m/s. After falling for time 5.9 s,

How fast is it moving? (Absolute value)

in m/s

Part 2

How far has it fallen? (Absolute value)

in m A student drops a rock off a bridge. The rock has a mass of 3.52 kg. If the bridge is 20.7 m high, how much time does it take it to reach the water below? in seconds

• You are supposed to show some effort before posting homework (or any other) problem. – Carl Witthoft Sep 19 '14 at 21:29

Hint 1: Everything accelerates (the velocity increases) downwards by 9.81 m/s, every second - on earth.

Hint 2: The relationship between height and velocity can be calculated using kinetic and potential energy equations:

0.5*m*v^2 = m*g*h

m = mass, v = velocity on the ground, g = gravity (9.81) and h = initial height.

Since you know the velocity increases by 9.81 per second you can make the formula v = g * t

t = time

So combining the two formulas, you should be able to calculate t based on a height.