Question

You see a leaf falling to the ground with constant speed. When you first notice it, the leaf has initial total energy PEi + KEi. You watch the leaf until just before it hits the ground, at which point it has final total energy PEf + KEf. How do these total energies compare? Ignore air resistance.
A. PEi + KEi > PEf + KEf
B. PEi + KEi = PEf + KEf
C. PEi + KEi < PEf + KEf
D. Impossible to tell from the information provided

Answer 1

Answer:

B. PEi + KEi = PEf + KEf        

Explanation:

It is given that

A leaf falling to the ground before hitting the ground has an initial total energy  of PEi + KEi.

And the total final energy of the leaf after it hits the ground is PEf + KEf .

Since there is no air resistance, therefore the total energy is conserved.

According to the conservation of law of conservation of energy, energy is neither created nor it is destroyed. The energy  is always conserved. The initial energy will be equal to the final energy.

Thus the total energy of the leaf before hitting the ground and after hitting the ground will be equal.

Thus initial energy is equal to the final energy.

Hence the answer is ---

B. PEi + KEi = PEf + KEf