Question

A shiny sports car at the top of a vertical cliff has a poten tial energy of 100MJ relative to the ground below. Unfortunately, a mishap occurs and it falls over the edge. When it is halfway to the ground, its kinetic energy is A. the same as the potential energy at that point. B. negligible. C. about 60 MJ. D. more than 60 MJ.

Answer 1

When car is at the top of the hill its whole energy is stored in the form of gravitational potential energy

$U = mgh$

so when height of the car becomes half then its potential energy is given as

$U_f = \frac{mgh}{2}$

so final potential energy when car falls down by half of the height will become half of the initial potential energy

So it is U = 50 MJ after falling down

Now by energy conservation we can say that final potential energy + final Kinetic energy must be equal to the initial potential energy of the car

So here at half of the height kinetic energy of car = 100 - 50 = 50 MJ

so we can say at this point magnitude of potential energy and kinetic energy will be same

A. the same as the potential energy at that point.