A 5.0-kg rock falls off of a 10 m cliff. If air resistance exerts a force of 10 N, what is the kinetic energy when the rock hits the ground? a. 400 J b. 12.6 m/s c. 100 J d. 500 J

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Answer 1 · 2017-11-22T04:51:16

#"400 J"#

Gravitational force acting on rock #= mg = 5.0 color(white)(.) "kg × 10 m/s² = 50 N"#

Net force on rock#= "50 N" - "10 N" = "40 N"#

By Work energy theorem
Work done by net force = Change in kinetic energy of rock

#F × S = K_f# ………[∵ Initial kinetic energy of rock is zero]

#"40 N × 10 m" = K_f#

#K_f = "400 J"#