Solving for Time and Velocity with Only Three Variables

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SUMMARY

The discussion focuses on solving physics problems involving projectile motion with limited variables. Specifically, it addresses two scenarios: Heather throwing a rock downwards at 20 m/s and Jerry throwing a rock upwards at the same speed, both from a height of 50 m. The key equations of motion, particularly the five standard kinematics equations, are essential for determining the time elapsed between the splashes and the velocity of a rock falling into a 10 m deep hole. The participants emphasize the importance of identifying the correct variable to solve for and suggest rearranging equations to include all necessary variables.

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  • Understanding of standard kinematics equations in physics
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  • Ability to manipulate algebraic equations
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Homework Statement



Physics: Only three variables and I don't know how to solve?
here is one problem: Heather and Jerry are standing on a bridge 50 m above a river. Heather throws a rock straight down with a speed of 20 m/s . Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air resistance. --- I need to find the time elapsed between the splashes.

A rock is tossed straight up with a velocity of +20 m/s. When it returns, it falls into a hole 10m deep. ----I need to find velocity and time for the rock at the moment it reaches the bottom of the hole .

For both of these I only have three variables, Velocity initial, change in X, and A. Should I assume that the V final is 0 in these?? otherwise I am confused. Thanks!

Homework Equations



all 5 standard kinematics


The Attempt at a Solution



The questions is conceptual...currently i cannot attempt an answer as far as I know.
 
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You have 3 variables, not including one variable that you want to find (work out what this one is first!) Then go through your 5 equations and use the one that includes all 4. You might have to do some rearranging!
 
The first of your questions is easier than it looks, if you see the trick...
 

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