2D Kinematics - 2 rocks off a bridge

AI Thread Summary
Heather and Jerry are on a bridge 60 meters above a river, where Heather throws a rock down at 14 m/s and Jerry throws one up at the same speed. To determine the time difference between the splashes, kinematic equations must be applied, considering their initial velocities and the acceleration due to gravity. Both rocks experience the same gravitational acceleration, but their different initial velocities will result in different final speeds upon impact with the water. The discussion emphasizes the need to identify all variables in the kinematic equations to solve the problem effectively.
kenji1992
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2D Kinematics -- 2 rocks off a bridge

Homework Statement



Heather and Jerry are standing on a bridge 60m above a river. Heather throws a rock straight down with a speed of 14m/s . Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air resistance.

a. How much time elapses between the first splash and the second splash?
b. Which rock has the faster speed as it hits the water?

Homework Equations





The Attempt at a Solution



H and J are 60 m above a river.
Heather throws the rock down with a speed, v=14 m/s
Jerry throws it up, v = 14 m/s

a. I'm assuming that I have to use some vertical/horizontal motion formula, but I don't know...
b. Don't they both have the same acceleration 9/8 m/s^2 so the same speed?
 
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kenji1992 said:
a. I'm assuming that I have to use some vertical/horizontal motion formula, but I don't know...
b. Don't they both have the same acceleration 9/8 m/s^2 so the same speed?

You will not need to worry about horizontal motion.
You are right that they will both have the same acceleration, but they both have different initial velocities.

Look for a kinematics equation that has everything you need. It should have...
v0, g, t, y0, y

You have already identified v0, g. What are t, y0, and y?
 
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