How Fast Does a Rock Fall from 20 Meters?

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SUMMARY

A rock with a mass of 0.2 kg dropped from a height of 20 meters strikes the ground at a velocity of 19.8 m/s. The calculations utilized the equations for kinetic energy (KE) and potential energy (PE), specifically KE = 1/2mv² and PE = mgh. The solution was confirmed as correct, with an emphasis on simplifying the problem by canceling mass (m) before substituting numerical values. This approach streamlines the calculation process and minimizes arithmetic errors.

PREREQUISITES
  • Understanding of kinetic energy (KE) and potential energy (PE) equations
  • Basic knowledge of gravitational acceleration (9.81 m/s²)
  • Ability to manipulate algebraic equations
  • Familiarity with units of measurement in physics
NEXT STEPS
  • Study the conservation of energy principles in physics
  • Learn about free fall and its implications in different gravitational fields
  • Explore the concept of air resistance and its effect on falling objects
  • Investigate the relationship between mass and acceleration in Newton's laws
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McNutt74
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Homework Statement


A rock with a mass of 0.2 kg is dropped from a height of 20 m. At what velocity does the rock strike the ground?

Homework Equations


KE= 1/2mv^2
PE=mgh

The Attempt at a Solution


0.2x9.81x20=1/2mv^2.
39.24=.1(v^2)
392.4=v^2
v=19.8 m/s
First time doing one of these problems, does my answer seem reasonable and did I use the right set of equations for this particular problem and did i set it up right? Thanks
 
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McNutt74 said:
First time doing one of these problems, does my answer seem reasonable and did I use the right set of equations for this particular problem and did i set it up right? Thanks
Looks good. Well done.

Note that if you'd done the math symbolically first (before plugging in any numbers) you could have saved some arithmetic:

1/2mv^2 = mgh

Note that the "m" cancels on either side.
 

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