A 2.0-kg mass is projected vertically upward from ground level with an initial speed of 30 m/s. The mass rises to a maximum height of 35 m above ground level. What is the change in mechanical energy of the mass caused by air resistance between the point of projection and the point of maximum height?
A) −0.21 kJ
B) −0.47 kJ
C) −0.40 kJ
D) −0.34 kJ
E) −0.69 kJ

Question

Quizplus · Accepted Answer

The change in mechanical energy is equal to the work done by air resistance, which is given by:$$W = Fd = mgd = (2.0 	ext{ kg})(9.8 	ext{ m/s}^2)(35 	ext{ m}) = -690 	ext{ J}$$The negative sign indicates that the work is done by air resistance, which reduces the mechanical energy of the mass. Therefore, the change in mechanical energy is:$$\Delta E = -W = -(-690 	ext{ J}) = \boxed{690 	ext{ J}}$$

A 20-Kg Mass Is Projected Vertically Upward from Ground Level with with an Initial