Kinetic energy re-
mechanical energy -ke+pe
potential energy
1. a baby carriage is sitting at the top of a hill that is 21 meters high. the carriage with the baby has a mass of 22kg.
calculate the potential energy of this situation,
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the cart
2. a cinder block is sitting on a platform 20 meters high and it contains 250 joules of potential energy. what is the mass
of this cinder block?
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3. there is a 18kg bell at the top of a tower that a certain height from the ground. if the potential energy is calculated to be
760 joules, determine the height of the tower.
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kinetic energy
4. what is the kinetic energy of a 55kg runner with a velocity of 14m/s? .
5. a car traveling on a road was found to have a kinetic energy of 69,759j. the car has a mass of 275kg. how fast was
this car traveling?
6. calculate the mass of a car that is travelling at a velocity of 38m/s and has a total energy of 12,700j.

1) The potential energy, P.E  = 4527.6 J

2) The mass, m = 1.28 kg

3) The height of the bell, h = 4.31 m

4)  The kinetic energy, K.E = 385 J

5) The velocity of the car, V = 22.53 m/s

6) The mass of the car,  m = 17.59 kg

Explanation:

1) The height of the hill, h = 21 m

The carriage with a baby has mass of, m = 22 kg

The potential energy,

                             P.E = mgh

                                   = 22 x 9.8 x 21

                                  = 4527.6 J

2) The height of the platform, h = 20 m

The P.E of the cinder block, P.E = 250 J

The mass,

                                m = P.E / gh

                                     = 250 / (9.8 x 20)

                                    = 1.28 kg

3) The mass of the bell, m = 18 kg

The P.E of the bell, P.E = 760 J

The height of the bell,

                            h = P.E/mg

                               = 760 / 18 x 9.8

                               = 4.31 m

4) The mass of the runner, m = 55 kg

The velocity of the runner, v = 14 m/s

The kinetic energy,

                              K.E = ½ mv²

                                     = ½ x 55 x 14

                                     = 385 J

5)The kinetic energy of the car, K.E = 69,759 J

The mass of the car, m = 275 kg

The velocity of the car,

                                 V = √(2K.E/m)

                                  V = √( 2 x 69759 / 275)

                                      = 22.53 m/s

6) The velocity of the car, v = 38 m/s

The kinetic energy of the car, K.E = 12700 J

The mass of the car,

                                m = 2 K.E/ v²

                                     = 2 x 12700 / 38²      

                                 m = 17.59 kg