A person holding a dog of mass 9.9 kg starts walking in a straight line for 5 m, then they walk up some stairs which have a length (not height) of 3 m and are placed at an angle 22° to the horizontal.
The total amount of work done by the person on the dog is:
What is the total power expended on the dog if the person walks at a constant speed of 0.85 m/s?
The total amount of work done by the person on the dog is:
What is the total power expended on the dog if the person walks at a constant speed of 0.85 m/s?
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Assuming the dog is not lifted or lowered, 0 Work in the 5 m of horizontal motion.
We need how high the dog was moved vertically.
Hypotenuse = 3 m
sin 22 = Y/3
Y = 1.12 m
Now the dog's change in Potential Energy
PE = MGH = 9.9 kg * 9.8 m/s^2 * 1.12 m = 109.03 Joules = Work
The person walked 5 + 1,12 = 6.12 m
distance = velocity * time
6.12 = 0.85 m/s * t
t = 7.2 s
Power = Energy/ time = 109.3 J / 7.2 s = 15.18 J/s = 15.18 Watt
We need how high the dog was moved vertically.
Hypotenuse = 3 m
sin 22 = Y/3
Y = 1.12 m
Now the dog's change in Potential Energy
PE = MGH = 9.9 kg * 9.8 m/s^2 * 1.12 m = 109.03 Joules = Work
The person walked 5 + 1,12 = 6.12 m
distance = velocity * time
6.12 = 0.85 m/s * t
t = 7.2 s
Power = Energy/ time = 109.3 J / 7.2 s = 15.18 J/s = 15.18 Watt