Elastic potential energy.
When you stretch a rubber band it has the "potential" to do work, to fly in a given direction. In doing so it changes it's elastic potential energy to kinetic energy.
The gas is in a rigid container: this means that its volume remains constant. Therefore, we can use Gay-Lussac law, which states that for a gas at constant volume, the pressure is directly proportional to the temperature. The law can be written as follows:

Where P1=5 atm is the initial pressure, T1=254.5 K is the initial temperature, P2 is the new pressure and T2=101.8 K is the new temperature. Re-arranging the equation and using the data of the problem, we can find P2:

So, the new pressure is 2 atm.
For an uniformly accelerated motion, we can write

where

is the acceleration of this motion, which in this problem is the gravitational acceleration, with a negative sign because it points downward, against the direction of the motion; h=0.540 m is the distance covered by the flea, and

is the initial velocity.
At the maximum height, the velocity is zero, so

. Therefore we can solve to find

:
Answer : B) The cow pulls back on the girl.
From newton’s third law we know that every action has a reaction force pushing back. So when the girl pulls on a cow, the cow is pulling back on her.
Answer:
0 N.
Explanation:
Force: This can be defined as the product of mass and the acceleration of the body. The S.I unit of force is Newton (N).
The expression of net force when both force act in the different direction is given as
F' = W-F ........................ Equation 1
Where F' = Net force on the bag, W = gravitational force on the bag, F = Force acting upward on the bag
Given: W = 18 N, F = 18 N.
Substitute into equation 1
F' = 18-18
F' = 0 N.
Hence the net force = 0 N.