Asled and rider with a combined mass of 140 kg are at the top of a hill of height 12.5 m above the level ground below. the sled is given a push providing an initial kinetic energy of 1550 j at the top of the hill. choosing a reference level at the bottom of the hill, what is the potential energy of the sled and rider at the top of the hill?

17150 J

Explanation:

m = 140 kg. h = 12.5 m , g = 9.8 m/s^2

The potential energy at the top of the hill is

U = m g h

U = 140 x 9.8 x 12.5 = 17150 J

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.