Question

Ball A is dropped from the top of a building and hits the ground in 10 seconds. Another ball B is thrown straight down from the same building one second after dropping ball A. Neglect air resistance and consider g - 9.8 m/s2 . What should be the initial velocity of ball B so that it hits the ground simultaneously with ball A: Select one: O a. 9.8 m/s b. 20.6 m/s c. 4.3 m/s d. 10.3 m/s

Answer 1

Answer:

d. 10.3 m/s

Explanation:

a = Acceleration due to gravity = 9.8 m/s²

t = Time taken to reach the ground

u = Initial velocity

s = Distance travelled

Distance ball A travels

$s=ut+\frac{1}{2}at^2\\\Rightarrow s=0t+\frac{1}{2}9.8\times 10^2\\\Rightarrow s=490\ m$

So, ball B would have to cover the same distance in 9 seconds as it is thrown after 1 second

$490=u\times 9+\frac{1}{2}9.8\times 9^2\\\Rightarrow \frac{490-\frac{1}{2}9.8\times 9^2}{9}=u\\\Rightarrow u=10.34\ m/s$

∴ Initial velocity of ball B is 10.3 m/s