How long does it take for a stone thrown from a bridge to hit the water below?

[Nitrate]

Homework Statement

A stone is thrown up at 30 m/s from the edge of a bridge 210 m above the river below. How many seconds elapse between toss and splash?

Homework Equations

The Attempt at a Solution

dv/dt=-9.8
v=-9.8t+c2
30=-9.8(0) + c1
c1=30

v=-9.8t+30
h=-4.9t^2+30t+c2
210=-4.9(0)^2+30(0)+c2
c2=210
h= -4.9t^2+30t+210

i'm not sure if I'm doing this right/what to do next if i am

 

[berkeman]

Homework Statement

A stone is thrown up at 30 m/s from the edge of a bridge 210 m above the river below. How many seconds elapse between toss and splash?

Homework Equations

The Attempt at a Solution

dv/dt=-9.8
v=-9.8t+c2
30=-9.8(0) + c1
c1=30

v=-9.8t+30
h=-4.9t^2+30t+c2
210=-4.9(0)^2+30(0)+c2
c2=210
h= -4.9t^2+30t+210

i'm not sure if I'm doing this right/what to do next if i am

Yes, your last equation looks okay to me. You've defined h=o at the surface of the water, which is fine. Solve for the time it takes for h to reach 0...