Question

A brick is released with no initial speed from the roof of a building and strikes the ground in 2.40s , encountering no appreciable air drag.

How tall, in meters, is the building?

How fast is the brick moving just before it reaches the ground?

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A rock is thrown vertically upward with a speed of 19.0m/s from the roof of a building that is 50.0mabove the ground. Assume free fall.

Part A

In how many seconds after being thrown does the rock strike the ground?

Part B

What is the speed of the rock just before it strikes the ground?

Answer 1

Answer:

Explanation:

height fallen = h , initial speed u = 0

time t = 2.4s

h = 1/2 x gt²

= .5 x 9.8 x 2.4²

= 28.22 m

Speed of striking the ground

v = gt

= 9.8 x 2.4

= 23.52 m/s

A ) When rock is thrown upwards

initial velocity u = - 19 m/s

g = 9.8 m/s²

h = ut + 1/2 gt²

50 = - 19t + .5 x 9.8 t²

4.9 t² - 19 t - 50 = 0

=5.7 s

B )

V = - -u+gt

= - 19 + 9.8 x 5.7

= 36.86 m/s