Core 3.31 MAIN PAGE

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Kinetic Energy

The term kinetic energy defines the energy of motion. An object which is in motion is said to have kinetic energy. If an object is not in motion it does not have kinetic energy. The following formula is used to calculate kinetic energy:

Problem:
A 55 kg man runs at a speed of 4 m/s. Find his kinetic energy.

Solution:

Step 1:

In this problem we are given the following: m = 55 kg v = 4 m/s

Step 2:

Plug the data into the given formula:

Answer: The man's kinetic energy is 440 J.

Problem:
A 300 kg car has a kinetic energy of 500 J. Find its speed.

Solution:

Step 1:

In this problem we are given the following:

m = 300 kg
KE = 500 J

Step 2:

Plug the data into the formula and solve the problem:

In order to solve for the speed we need to take the square root of (3.3 m²/s²)

Answer: The speed of the car is 1.82 m/s.

Problem:
An object is moving at a speed of 20 m/s and has a kinetic energy of 10,000 J.  What is the mass of the object?

Solution:

Step 1:

In this problem we are given the following:

v = 20 m/s
KE = 10,000 J

Step 2:

Plug the data into the formula:

In order to find the mass we need to divide both parts of the equation by 7200.

Answer: The mass of an object is 50 kg.