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

Explanation:The change in mechanical energy is equal to the work done by air resistance, which is given by:$$W = Fd = mgd$$where:* F is the force of air resistance* d is the distance over which the force acts* m is the mass of the object* g is the acceleration due to gravityIn this case, the distance over which the force acts is equal to the maximum height reached by the object, which is 35 m. The force of air resistance is equal to the weight of the object, which is:$$F = mg = (2.0 	ext{ kg})(9.8 	ext{ m/s}^2) = 19.6 	ext{ N}$$Therefore, the change in mechanical energy is:$$W = Fd = (19.6 	ext{ N})(35 	ext{ m}) = 686 	ext{ J}$$Converting to kilojoules, we get:$$W = 686 	ext{ J} = 0.686 	ext{ kJ}$$Therefore, the correct answer is A) 0.686 kJ.

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