Answer:
Potential energy plus kinetic energy equals mechanical energy because mechanical energy is basically just all of an object's energy, it's just two kinds of energy. The potential is stored inside and kinetic is being used. Both of those together is the total amount of the objects energy, which is the mechanical energy.
Explanation:
Probably because the earth is stationary rotating on its axis whereas the baseball is the one doing all of the movement after being thrown
Answer:

Acceleration, in m/s, of such a rock fragment = 
Explanation:
According to Newton's Third Equation of motion

Where:
is the final velocity
is the initial velocity
a is the acceleration
s is the distance
In our case:

So Equation will become:

Acceleration, in m/s, of such a rock fragment = 
Answer:
E = 0.01 J
Explanation:
Given that,
The mass of the cart, m = 0.15 kg
The force constant of the spring, k = 3.58 N/m
The amplitude of the oscillations, A = 7.5 cm = 0.075 m
We need to find the total mechanical energy of the system. It can be given by the formula as follows :

Put all the values,

So, the value of total mechanical energy is equal to 0.01 J.
Answer:
1. a) 72 N.
2. a) 2 m/s².
Explanation:
Given the following data;
1. Mass = 90kg
Acceleration = 0.8 m/s²
To find the force;
Force = mass * acceleration
Force = 90 * 0.8
Force = 72 Newton.
2. Mass = 50kg
Force = 100N
To find the magnitude of acceleration;
Acceleration = force/mass
Acceleration = 100/50
Acceleration = 2 m/s²