Explanation:
C is correct.
Newton second law states that force is directly proportional to acceleration with m being the constant of variation.

So


A is wrong, the constant g only happens in free fall or in vertical direction
B and D are wrong due to the mathematical error or equation error
Answer:
Electrical energy. Jump to navigation Jump to search. Electrical energy is energy derived from electric potential energy or kinetic energy. When used loosely, electrical energy refers to energy that has been converted from electric potential energy
Explanation:
The acceleration due to gravity of Mars is 
<u>Explanation:</u>
As per universal law of gravity, the gravitational force is directly proportional to the product of masses and inversely proportional to the square of the distance between them. But in the present case, the gravity need to be determined between Mars and the object on Mars. Since the mass of Mars is greater than the mass of any object. Thus,

Here, G is the gravitational constant, R is the radius of Mars and M, m is the mass of Mars and the object respectively..
Also, according to Newton’s second law of motion, the acceleration of any object will be equal to the ratio of force exerted on it to the mass of the object.
So in order to determine the acceleration due to gravity of Mars, divide the gravitational force of Mars by mass of object on the surface of Mars.




B. Ptolemy believed that the earth was the center of the universe
<h2>
Answer:</h2>
<u>Friction:</u>
When an object slips on a surface, an opposing force acts between the tangent planes which acts in the opposite direction of motion. This opposing force is called Friction. Or in other words, Friction is the opposing force that opposes the motion between two surfaces.
The main component of friction are:
<u>Normal Reaction (R):
</u>
Suppose a block is placed on a table in the above picture, which is in resting state, then two forces are acting on it at that time.
The first is due to its weight mg which is working from its center of gravity towards the vertical bottom.
The second one is superimposed vertically upwards by the table on the block, called the reaction force (P). This force passes through the center of gravity of the block.
Due to P = mg, the box is in equilibrium position on the table.
<u>Coefficient of friction ( </u>μ )<u>:
</u>
The ratio of the force of friction and the reaction force is called the coefficient of friction.
Coefficient of friction, µ = force of friction / reaction force
μ = F / R
The coefficient of friction is volume less and dimensionless.
Its value is between 0 to 1.
<u>Advantage and disadvantage from friction force:
</u>
- The advantage of the force of friction is that due to friction, we can walk on the earth without slipping.
- Brakes in all vehicles are due to the force of friction.
- We can write on the board only because of the force of friction.
- The disadvantage of this force is that due to friction, some parts of energy are lost in the machines and there is wear and tear on the machines.
<u>How to reduce friction:
</u>
- Using lubricants (oil or grease) in machines.
- Friction can be reduced by using ball bearings etc.
- Using a soap solution and powder.