Question

A 100 gram apple is released from rest 500 m above the ground. Due to the combined forces of air resistance and gravity, it has a speed of only 40 m/s when it reaches the ground. How much work must have been done on the apple by the force of air resistance?

(A) 80 J

(B) 420 J

(C) 500 J

(D) 580 J

Answer 1

$\Delta W=\frac{mv^2}{2}-mgh=\frac{0.1\cdot 40^2}{2}-0.1\cdot10\cdot 500=-420\ (J)$

$(B)\ 420\ J$ . Answer