QOD 97 Explain what it means when an object accelerates at a rate of 2 m/s2? When an object accelerates at a rate of 2 m/s2 it means that every second, the speed increases by 2 m/s.

QOD 97 4-22-14 1. Explain what it means when an object accelerates at a rate of 2 m/s2? When an object accelerates at a rate of 2 m/s2 it means that every second, the speed increases by 2 m/s. 2. What is the acceleration of a cheetah that is running a velocity of 28 m/s and slows down to 20 m/s after 10 seconds? (Write equation & show steps) a = vf – vi a = 20 m/s – 28 m/s = - .8 m/s t 10 s 10 s a = - 0.8 m/s2

Go over answers to finding acceleration

Calculating Potential & Kinetic Energy Potential Energy – stored energy of an object due to its state or position Kinetic Energy – energy of a moving object Unit – Joules (J)

1 Joule of Energy … the energy required to lift a small apple (with a mass of approximately 100 g) vertically through one meter of air. the energy released when that same apple falls one meter to the ground. the kinetic energy of a 50 kg human moving very slowly (0.2 m/s).

(Gravitational) Potential Energy PE = mgh Mass(kg) x Gravity x Height(m) = ___ Joules (J) Acceleration due to Gravity = 9.8 m/s2

Ex: 1 PE = mgh PE = 2.5 kg x 9.8 m/s2 x 2 m = A box that has a mass of 2.5 kg is sitting on a shelf that is 2 meters high. What is the gravitational potential energy of the box? Mass = 2.5 kg Gravity = 9.8 m/s2 Height = 2 m PE = mgh PE = 2.5 kg x 9.8 m/s2 x 2 m = PE = 49 Joules (J)

PE = 6,468 Joules Ex: 2 PE = mgh PE = 55 kg x 9.8 m/s2 x 12 m = A boy has a mass of 55 kg. He climbs 12 meters up a tree. What is his gravitational potential energy? Mass = ________ Gravity = ________ Height = _______ PE = 6,468 Joules 55 kg 9.8 m/s2 12 m PE = mgh PE = 55 kg x 9.8 m/s2 x 12 m =

Ex: 3 Find the gravitational potential energy of a pencil sitting on the edge of a desk. The pencil is 0.25 kg and the desk is 0.78 m high. PE = mgh PE = .25 kg x 9.8 m/s2 x .78 m = PE = 1.911 J

Ex: 3 - challenge Find the gravitational potential energy of a pencil sitting on the edge of a desk. The pencil is 25 g and the desk is 78 cm high. Convert 25 g to ____ kg Convert 78 cm to ____ m PE = mgh PE = .025 kg x 9.8 m/s2 x .78 m = PE = 0.191 J .025 .78

Kinetic Energy KE = 0.5xmv2 0.5 x Mass(kg) x Velocity(m/s) 2 = ___ Joules

Ex4: Determine the kinetic energy of a 55 kg woman running with a speed of 3.87m/s. KE = 0.5 x mv 2 KE = 0.5 x 55 x (3.87) 2 KE = 0.5 x 55 x 14.97 KE = 411.9 Joules

Ex5: What is the kinetic energy of a cheetah with a mass of 72 kg running a speed of 29 m/s. KE = 0.5 x mv 2 KE = 0.5 x 72 x (29) 2 KE = 0.5 x 72 x 841 KE = 30,276 Joules

Ex6: What is the kinetic energy of a pencil with a mass of 0 Ex6: What is the kinetic energy of a pencil with a mass of 0.25 kg thrown a speed of 10 m/s. KE = 0.5 x mv 2 KE = 0.5 x 0.25 x (10) 2 KE = 0.5 x 0.25 x 100 KE = 12.5 Joules

Practice WS

Ex 4: (Create your own problem!) With your partner, write a word problem that tells the mass and height of your object/person. Draw a simple diagram of your word problem. Solve your problem to find the gravitational potential energy of your object/person, but don’t write down the answer! Pass the problem to your neighbors to solve.

KE = ½ x mass x velocity

Take Pictures!! With a partner… Take 3 pictures of kinetic energy At least 1 must include a person Take 3 pictures of potential energy