Question

Fleas have remarkable jumping ability. A 0.45 mg flea, jumping straight up, would reach a height of 30 cm if there were no air resistance. In reality, air resistance limits the height to 20 cm .
Part A What is the flea's kinetic energy as it leaves the ground?
Part B At its highest point, what fraction of the initial kinetic energy has been converted to potential energy?Express your answer using two significant figures.

Answer 1

Answer:

A) $1.35*10^{-6}J$

B) 0.67

Explanation:

If there would be no air resistance:

$Vf^2=Vo^2-2*g*h$

$0=Vo^2-2*10*0.3$

$Vo=\sqrt{6} m/s$

So, its initail kinetic energy is:

$Ko = m/2*Vo^2=0.45/10^6/2*6=1.35*10^{-6}J$

Its final potential energy is:

$Uf = m*g*h = 0.45/10^6*10*0.2=0.9*10^{-6}J$

The fraction of the potential energy is:

Fraction = Uf/Ko = 0.67

This means that one third of its initial energy is lost.