posted by Danielle on .
A person stands on a bridge that is 100 feet above a river.
If she drops a pebble how fast is it moving after 2 seconds?
How long does it take the pebble to reach the river below?
She has another pebble that she tosses up with initial speed of 8 feet per second. It goes up, then starts falling down to the river below. By the time it reaches the river what is its speed?
vf=vi+gt for the firstquestion
second question: h=vi*t-4.9t^2 Vi=0, solve for t
solve for time t, then vf=vi-9.8t
but there is an easier method for the last:
vf^2=vi^2+2ad where a=-9.8, d=-100