Physics Projectile Motion Help
Hey, I'm having trouble with this one problem, "A stone is thrown outward from the top of a cliff that's 59.4 meters tall with an upward velocity of 19.5 meters per second. How long is the stone in the air?" I know the answer is 6 I just don't quite know how to get there.
December 20, 2013
4 Comments • Newest first
Um, with no air resistance, H = (-9.8/2)t^2 + 19.5t + 59.4
Find the positive zero of H and that is 6.
Physics is so dumb.
You have to find the distance it travels up. With the initial velocity as 59.4 and gravity as acceleration, and 0 as final velocity.
After that, calculate the time it will take to travel down. Using 0 as initial velocity, gravity as acceleration, and the distance you found going up + the cliff's height.
s=59.4m
u=19.5m/s up
a=9.8m/s^2 down
t=?
s=ut+1/2a(t^2)
(i am setting down to be positive, you have to state either up or down as positive)
4.9t^2-19.5t-59.4=0 solve for t
t=-2.02 or 6
Reject -2.02 as time must be positive.
so t=6s