From a balloon moving upwards with a velocity of 12 `ms^(-1)`, a packet is released when it is at a height of 65 m from the ground. The time taken by it to reach the ground is
(take, g = 10 `ms^(-2)`)

Options

A. 5 s
B. 8 s
C. 4 s
D. 7 s

Answer

B

Explanation

Given, `u=12 ms^(-1)`
`s=-65m`
`rArrg=-10 ms^(-2)`
We know that, `s=ut+1/(2)g t^(2)`
`rArr-65=12t-1/(2)xx10t^(2)`
`-65=12t-5t^(2)`
`5t^(2)-12t-65=0`
`5t^(2)-25t+13t-65=0`
`5t(t-5)+13(t-5)=0`
`(5t-13)(t-5)=0`
`rArrt=-13/(5)Sort=5s`
Time taken by balloon to reach on ground t = 5s