Explanation:
Given that,
The mass of rock, m = 2.35-kg
It was released from rest at a height of 21.4 m.
(a) The kinetic energy is given by : 
As the rock was at rest initially, it means, its kinetic energy is equal to 0.
(b) The gravitational potential energy is given by : 
It can be calculated as :

(c) The mechanical energy is equal to the sum of kinetic and potential energy such that,
M = 0 J + 492.84 J
M = 492.84 J
Hence, this is the required solution.
The answer is 9.8 ms^-2, because there is only one force acting on the object so the acceleration will be numerically equal to the gravitational field strength.
The bag moves to the left.
This is because of Newton's third law of motion that states:
For every action force on a body, there is an opposite and equal reaction force.
Thus pushing the bag from the right makes it move to the left.
Answer:
a) m=20000Kg
b) v=0.214m/s
Explanation:
We will separate the problem in 3 parts, part A when there were no coals on the car, part B when there is 1 coal on the car and part C when there are 2 coals on the car. Inertia is the mass in this case.
For each part, and since the coals are thrown vertically, the horizontal linear momentum p=mv must be conserved, that is,
, were each velocity refers to the one of the car (with the eventual coals on it) for each part, and each mass the mass of the car (with the eventual coals on it) also for each part. We will write the mass of the hopper car as
, and the mass of the first and second coals as
and
respectively
We start with the transition between parts A and B, so we have:

Which means

And since we want the mass of the first coal thrown (
) we do:



Substituting values we obtain

For the transition between parts B and C, we can write:

Which means

Since we want the new final speed of the car (
) we do:

Substituting values we obtain

That is called a physical trainer or a fitness coach. Hope I helped!