1. Work, Energy and Power Kinetic Energy

2. Kinetic energy is the energy of motion. An object which has motion - whether it be vertical or horizontal motion - has kinetic energy. There are many forms of kinetic energy - vibratory (the energy due to vibratory motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another).

3. Continued The amount of translational kinetic energy (from here on, the phrase kinetic energy will refer to translational kinetic energy) which an object has depends upon two variables: the mass (m) of the object and the speed (v) of the object.

4. Continued The following equation is used to represent the kinetic energy (E K ) of an object E K = ½ mv 2 m = mass v = velocity This equation reveals that the E K of an object is directly proportional to the square of its speed. That means that if speed doubles, the E K will increase by a factor of four

5. KE continued Kinetic energy is a scalar quantity; it does not have a direction. Unlike velocity, acceleration, force, and momentum, the kinetic energy of an object is completely described by magnitude alone. Like work and potential energy, the standard metric units of measurement for kinetic energy is the Joule.

6. Example 1 Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s. E K = ½ mv 2 = ½ (1000kg)(20.0m/s) 2 = 200 000 Joules = 2.00 x 10 5 Joules or 200 kJ

7. Example 2 If the roller coaster car in the above problem were moving with twice the speed, then what would be its new kinetic energy? E K = ½ mv 2 = ½ (1000kg)(40.0m/s) 2 = 800 000 Joules = 8.00 x 10 5 Joules or 800 kJ

8. Example 3 Missy Diwater, the former platform diver for the Ringling Brother's Circus had a kinetic energy of 15kJ just prior to hitting the bucket of water. If Missy's mass is 50 kg, then what is her speed? E K = ½ mv 2 15 000 J = ½ (50kg)v 2 2(15000) = 50v 2 30000 = v 2 50 v =24.5m/s

9. Example 4 Calculate the velocity of a fist with a mass of 750g while being slammed into a board with a force of 50 N over a distance of 35 cm.(watch out for units!) E K = W = ½ mv 2 W = F d = ½ (0.75kg) v 2 50 N x 0.35 m = ½ (0.75kg) v 2 17. 5/ 0.375 = v 2 6.83 m/s = v