A roller coaster car with a mass of 17,690 kg is moving at a speed of 5 m/s over a hill that is 87.4 m above the ground. What is the total mechanical energy of the car-Earth system?

Explanation:

Given that,

The mass of the car, m = 17,690 kg

The speed of the car over the hill, v = 5 m/s

The car is 87.4 m above the  ground.

We need to find the total mechanical energy of the car-Earth system. Mechanical energy is equal to the sum of kinetic energy and potential energy. So,

So, the total mechanical energy of the car-Earth system is .

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.