2D Kinematics - 2 rocks off a bridge

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SUMMARY

This discussion focuses on a 2D kinematics problem involving two rocks thrown from a bridge 60 meters above a river. Heather throws her rock straight down at an initial speed of 14 m/s, while Jerry throws his rock straight up with the same initial speed. The key equations of motion must be applied to determine the time difference between the splashes and the final speeds of both rocks upon impact with the water. The rocks experience the same gravitational acceleration of 9.8 m/s², but their differing initial velocities result in different final speeds.

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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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