Question

Consider two cars **A** and **B**. Car
**A** is raised to some height h inside a service
station, and car **B** is speeding down the highway.
Describe the potential, kinetic, and total energies of each car.
How much work is used to raise **A** to height h? What
happens to the kinetic energy of **B** if its speed is
doubled?

Would car **A** gravitational potential energy
because work is done in elevating it?

Please help! Physics is like a complete foreign language to me and I've been trying to figure this question out for days to no avail! Any assistance you can offer would be greatly appreciated!

Answer #1

For car A:

Its Potential energy(P.E) is equal to = m*g*h <----- assuming the ground level as the Zero Potential level

g = 9.8 m/s2

Its Kinetic energy(K.E) is 0 <---- assuming it is static at that point

So, total energy = mgh + 0 = mgh

Now, for B :

P.E = m*g*h'

where h' = height above which the car is located from the ground

K.E = 0.5*mv^2

where v = speed of the car B at that instant

So, total energy = mgh' + 0.5*mv^2

Now, work done to raise A to height h = -m*g*h <------ NOTE the -ve sign due to gravity acting downwards

Kinetic energy is proportional to v^2 . So if speed is doubled, the Kinetic energy will quadruple (4 times)..

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