Algebra Problem?????

Question

The distance an object falls when dropped from rest is given by the formula d = 4.9t2 where d is distance in metres and t is time in seconds. An object is dropped from a height of 122.5 m. How long will it take to hit the ground?

Answer 1

By your formula:

t=sqr(122.5/4.9) = 5 s

By the s=1/2*a*t^2

where a=9.8m/s^2

t=sqr(2*122.5/9.8) = 5 s

Answer 2

well you know d = 4.9 t^2

and you know d = 122.5 m .. so:

122.5=4.9 t^2

t^2 = 122.5/4.9

t^2 = 25

t= +- sqrt(25)

so t= 5 or t=-5

since time cannot be negative you know the time is 5seconds