Question

Shaila is riding on a rollercoaster when her phone falls out of her pocket. The phone followed the equation y=−16t2+400

where y
gives the height of the phone after t
seconds. How long did it take her phone to hit the ground?

The phone hit the ground after seconds.

Answer 1

5 seconds

Explanation:

y =
`-16t^(2) + 400 \\`

Make t the subject:

`16t^(2) = -400\\t^(2) = (400)/(16) = 25\\ t = √(25) = 5`

Therefore the answer is 5 seconds

Answer 2

5 seconds

Explanation:

when the phone hits the ground then y = 0 , that is

- 16t² + 400 = 0 ( subtract 400 from both sides )

- 16t² = - 400 ( divide both sides by - 16 )

t² = 25 ( take square root of both sides )

t =
`√(25)` = 5

the phone hits the ground after 5 seconds