1. B2.3
Kinetic Energy
and Motion

2. Kinetic Energy Kinetic energy is energy due to motion.
Any moving object that has mass, has kinetic energy.
The kinetic energy of an object varies directly as its mass.
So, for example, if you double the mass of an object, its kinetic energy will double.
= kinetic energy (J)
m = mass (kg)
The kinetic energy of on object varies directly as the square of its speed.
v = speed (m/s)
This is a “direct squared” relationship!
So, for example of you double the speed of an object, its kinetic energy will increase by a factor of four.

3. examples: Practice Problems p. 179
4) Calculate the kinetic energy of an electron with a mass of 9.11 x kg moving at a uniform speed of 2.00 x 105 m/s.
1.82 x J
5) A small toy moving horizontally at a uniform speed of 2.2 m/s has a kinetic energy of 18 J. Calculate the mass of the toy.
7.4 kg
6) A baseball with a mass of 300 g has a kinetic energy of 304 J. Calculate the speed of the baseball.
45.0 m/s
7) A moving toy with a mass of 7.4 kg has a kinetic energy of 18 J. Calculate the speed of the toy.
2.2 m/s

4. Homework: read pages 179 – 181 B2.3 Check and Reflect
page 182 #’s 1 – 7, 10(a thinker!)