Speed distance and not a lot of hair left

[steveandy2002]

Homework Statement

a balls inital velocity is 72 km/ph and falls 100 meters with gravity @ 10 meters per second and i need to work out the time it takes to fall to ground. i was given s=ut+0.5*gt^2

Homework Equations

s=ut+0.5gt^2
v^2=u^2+2as
t=(v-u)/a

The Attempt at a Solution

v2=u2+2as
v=squr u^2+2as
v=squr 20^2+2*10*100
v=48.98979486

t=(v-u)/a
t=(48.98979486-20)/10
t=2.898979486 seconds

100=20*2.898979486+0.5*10*2.898979486^2

is this correct??
and is there a way to do this with just the s=ut+0.5at^2 formula ?

 

[tiny-tim]

hi steveandy2002!

(try using the X² button just above the Reply box )

a balls inital velocity is 72 kph and falls 100 meters with gravity @ 10 meters per second and i need to work out the time it takes to fall to ground.
…
and is there a way to do this with just the s=ut+0.5at^2 formula ?

s = 100, u = 72, a = 10 …

what's the difficulty? ​

 

[steveandy2002]

hi steveandy2002!

(try using the X² button just above the Reply box )


s = 100, u = 72, a = 10 …

what's the difficulty? ​

not sure what you mean, i need to get time not s

 

[tal444]

All you need to do is plug in your known values into s=ut+\frac{1}{2}gt². Then you move everything to one side and solve the quadratic equation. What are you having issues with?

 

[Chestermiller]

Don't forget to change the units on u from km/hr to m/s.