Question

A brick is dropped (zero initial speed) from the roof of a building. The brick strikes the ground in 1.90 s. You may ignore air resistance, so the brick is in free fall. (a) How tall, in meters, is the building? (b) What is the magnitude of the brick’s velocity just before it reaches the ground? (c) Sketch ay-t, vy-t, and y-t graphs for the motion of the brick.

Answer 1

Answer: Height of building = 17.69m, velocity of brick = 18.6m/s

Explanation: From the question, the body has a zero initial speed, thus initial velocity (u) all through the motion is zero.

By ignoring air resistance makes it a free fall motion thus making it to accelerate constantly with a value of $a = 9.8m/s^{2}$.

Time taken to fall = 1.90s

a)

thus the height of the building is calculated using the formulae below

$H = ut + \frac{1}{2} gt^{2}$

but u = 0 , hence

$H = \frac{1}{2} gt^{2}$

$H = \frac{1}{2} *9.8* 1.9^{2} \\\\H = 17.69m$

b)

to get the value of velocity (v) as the brick hits the ground, we use the formulae below

$v^{2} = u^{2} + 2aH$

but u= 0, hence

$v^{2} = 2gH$

$v^{2} = 2 * 9.8 * 17.69\\v = \sqrt{2 *9.8* 17.69} \\v = 18.62m/s$

 

find the attachment in this answer for the accleration- time graph, velocity- time graph and distance time graph