Question

a feather of mass 0.001 kg falls from a height of 2 m. under realistic conditions, it experiences air resistance. based on what you know about friction, what can you say about the kinetic energy of the feather as it reaches the ground? acceleration due to gravity is ( g = 9.8 , \text{m/s}^2 ).

○ a ( ke = 0.0196 , \text{j} )
○ b ( ke = 0 , \text{j} )
○ c ( ke > 0.0196 , \text{j} )
○ d ( ke < 0.0196 , \text{j} )

Explanation:

Step1: Calculate potential energy without air resistance

The formula for gravitational potential energy is \(PE = mgh\). Given \(m = 0.01\space kg\), \(g=9.8\space m/s^{2}\), and \(h = 2\space m\).

$$PE=(0.01\space kg)\times(9.8\space m/s^{2})\times(2\space m)=0.196\space J$$

Step2: Consider the effect of air resistance

In the absence of air resistance, by the conservation of mechanical energy \(KE = PE\) (at the ground, potential energy is converted to kinetic energy). But when there is air resistance, some of the initial potential energy is dissipated as heat (due to work done against air - resistance). So \(KE\lt PE\)

Answer:

D. \(KE < 0.196\space J\)