How Fast Does a Rock Fall from 20 Meters?

So you're left with:1/2v^2 = ghNow plug in numbers:1/2v^2 = 9.81*20And solve for v:v^2 = 196.2v = sqrt(196.2) = 19.8 m/sIn summary, a rock with a mass of 0.2 kg, dropped from a height of 20 m, will strike the ground at a velocity of 19.8 m/s. This is calculated using the equations KE= 1/2mv^2 and PE=mgh. The answer seems reasonable and the equations were used correctly. It was also noted that the problem could have been solved symbolically first to
  • #1
McNutt74
1
0

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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  • #2
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.
 

What is mechanical energy?

Mechanical energy refers to the energy that an object possesses due to its motion or position. It is the sum of an object's kinetic energy (energy of motion) and potential energy (energy of position).

How do you calculate mechanical energy?

Mechanical energy can be calculated by adding the kinetic energy and potential energy of an object. The formula for mechanical energy is ME = KE + PE.

What is the law of conservation of mechanical energy?

The law of conservation of mechanical energy states that in a closed system, mechanical energy remains constant. This means that the total amount of mechanical energy in a system is conserved and does not change, even if it is transformed from one form to another.

What are some examples of mechanical energy problems?

Examples of mechanical energy problems include calculating the kinetic energy of a moving object, determining the potential energy of an object at a certain height, and solving for the mechanical energy of a system before and after a collision.

How is mechanical energy related to work and power?

Mechanical energy is related to work and power because work is defined as the transfer of energy from one object to another, and power is the rate at which work is done. Mechanical energy plays a role in both work and power calculations, as it is the energy that is being transferred.

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