Question

A stone is dropped from the upper observation deck of a tower, 300 m above the ground (Assume g=9.8m/s^2)

If the stone is throw downward with a velocity of 3m/s, how long does it take to reach the ground (round to 2 decimal places).

Answer 1

7.45 s

Explanation:

Given:

h₀ = 300 m

g = -9.8 m/s²

v₀ = -3 m/s

h = 0 m

`\boxed{h=h_0+v_ot+(1)/(2) gt^2}`

`0 = 300+(-3)t+(1)/(2) (-10)t^2`

`0=300-3t-5t^2`

`5t^2+3t-300=0`

`\boxed{x=(-b\pm√(b^2-4ac) )/(2a) }`

`t=(-3\pm√(3^2-4(5)(-300)) )/(2(5))`

`=(-3\pm√(6009) )/(10)`

`t=7.45\ s`