Question

Write the answer to this question. Energy is measured in units called joules(J). Suppose a roller coaster car starts with 78,000 J of potential energy. In a few seconds, it converts two-thirds of this energy into kinetic energy. As it takes a curve, the car doubles its kinetic energy. How much mechanical energy does the car now have?

Answer 1

Answer:78,000 J

Explanation:

Given

Initial Potential Energy P=78,000 J=78 kJ

Total Energy=Potential Energy+Kinetic Energy

initially kinetic energy is zero therefore

Total Energy=Potential Energy

If two-thirds of this energy converts to kinetic Energy

i.e. kinetic Energy $=\frac{2}{3}\times 78=2\times 26=52 kJ$

As it take curve its kinetic Energy doubles i.e.$2\times 52=104 kJ$

but total Energy is constant i.e. 78 kJ

therefore there must be a decrease in Potential energy of coaster

78=104+P.E.

P.E.=-26 kJ

Mechanical Energy of car is =sum of kinetic and Potential Energy

=78 kJ=78,000 J