Question

If a roller coaster car had 40,000 J of gravitational potential energy when at rest on the top of a hill how much kinetic energy does it have when it is 3/4 of the way down the hill

Answer 1

Answer:

K.E = 30,000 J

Explanation:

Given,

The potential energy of the roller coaster car, P.E = 40000 J

The kinetic energy at height h/4, K.E = ?

According to the law of conservation of energy, the total energy of the system is conserved.

At height 'h', the total energy is,

                                    P.E = mgh

                                     K.E = 0

At height 'h/4', the total energy is

                                     P.E + K.E = mgh

                                     P.E = mgh/4

                                     K.E = 1/2 mv²

Therefore,

                                   mgh/4 + 1/2 mv² = mgh

                                    gh/4 + v²/2 = gh

Hence,

                                      v² = 3gh/2

Substituting in the K.E equation

                               K.E = 1/2 mv²

                                      = 1/2 m (3gh/2)

                                       = 3/4 mgh

                                        = 3/4 x 40000

                                         = 30000 J

Hence, the K.E of the roller coaster car is, K.E = 30000 J