You have changed a roof top air conditioner of a 75 m tall building and drag the

Question

You have changed a roof top air conditioner of a 75 m tall building and drag the 200 kg old unit 50 m to the edge of the roof by pulling on a rope that makes a 25 degree angle to the roof. You pull with 150 N & it takes 35 s to do this, (a) How much work is done dragging the old unit? (b) How much power is this work? (c) How much Potential Energy does the unit have in ref to the ground? (d) What is the Kinetic Energy of the unit at this point? (e) You push the unit off the roof - how much time does it take to hit the ground? (f) What is the Potential Energy as it hits the ground? (g) What is the velocity as it hits the ground? (h) What is the Kinetic Energy of the unit as it hits the ground? (Use the rest of this page and the back of the paper for your calculations.)

Explanation / Answer

a) work done = 150 * cos25 * 50

                        = 6797.3 J

b) power = 6797.3/35 = 194.2 W

c) potential energy = 200 * 9.8 * 75 = 147000 J

d) kinetic energy at this point   =   6797.3 J

e)    time taken to hit ground = sqrt(2 * 75/9.8)

                                                  = 3.91   sec

f)    potential energy as it hit ground = 0 J

g)     velocity with which it hit ground = 9.8 * 3.91 = 38.318 m/sec

h)    kinetic energy with which it hit ground = 147000 J

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