Answer:
<em>Both energies are equal when the rock has fallen 20 m or equivalently when it is at a height of 20 m.</em>
Explanation:
<u>Potential and Kinetic Energy</u>
The gravitational potential energy is the energy an object has due to its height above the ground. The formula is

Where:
m = mass of the object
g = acceleration of gravity (9.8~m/s^2)
h = height
Note we can also use the object's weight W=mg into the formula:

The kinetic energy is the energy an object has due to its speed:

Where v is the object's speed.
Initially, the object has no kinetic energy because it's assumed at rest.
The W=30 N rock falls from a height of h=40 m, thus:

Since the sum of the kinetic and potential energies is constant:
U' + K' = 1,200 J
Here, U' and K' are the energies at any point of the motion. Since both must be the same:
U' = K' = 600 J
U'=Wh'=600
Solving for h':

Both energies are equal when the rock has fallen 20 m or equivalently when it is at a height of 20 m.
Answer:
The answer is "Rigor mortis".
Explanation:
When the very large volume will be that the progress of its postponed by calcium and magnesium. The causes brain intensification of a liver due to the change throughout the myofibrils within a week of dying of its organism. When anyone accidentally spilled a power cable into a rank for toads, one's tissue will be disrupted instantly by stringent deaths.
The atomic number is a neutron
Answer:
C
Sign-Negative
Explanation:
We are given that
Electric field =
(Radially downward)
Acceleration=
(Upward)
Mass of charge=3 g=
kg
1kg=1000g
We have to find the magnitude and sign of charge would have to be placed on a penny .
By newton's second law


Substitute the values then we get

Substitute the values then we get




C
Sign of charge =Negative
Because electric force acting in opposite direction of electric field therefore,charge on penny will be negative.