Physics Help: Power Problem?
Topic: Physics Help: Power Problem?
July 19, 2019 / By Rose Question:
I solved part A but cant solve part B. Thanks for help
A skier of mass 70.8 kg is pulled up a slope by a motor-driven cable.
(a) How much work is required for him to be pulled a distance of 59.2 m up a 30.4° slope (assumed frictionless) at a constant speed of 1.94 m/s?
This I found to be 20.785 kJ
b) A motor of what power is required to perform this task
Answer in hp
Best Answers: Physics Help: Power Problem?
Muriel | 6 days ago
If it pulls him 59.2 meters at 1.94 meters per second, it takes
59.2 / 1.94 = 30.5 seconds
20.8 kjoules in 30.5 seconds is 0.681 kwatts 0r 681 watts.
1 hp = 746 watts, to this is 681/746 = 0.91 HP
👍 120 | 👎 6
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Originally Answered: PHYSICS QUESTION about work and power?
Work: force exerted over a distance: F x d
Power: how much work per second
since work is an energy we can say W = -U (where U is potential energy)
U = mgh, at the top of the hill U = (56kg)(-9.8m/s2)(30.5m) = -16738.4 Joules
so W = 16738.4 Joules
now since you know how long it takes to get up to the top (10s) divide work by time to get power
P = W/t = 16738.4 Joules/10 seconds = 1673.84 Watts or approximately 1.7 kiloWatts
Power is work divided by time. Your time is ( 59.2 m ) / ( 1.94 m/s ) = 30.5 seconds, so the power is ( 20.785 kJ ) / ( 30.5 sec ) = 681 Watts. Now convert that to horsepower: 1 hp = 746 Watts.
👍 40 | 👎 -1
Power = Work/Time
You can find time from part (a)
=> Distance = speed*time
=> time = distance/speed = 59.2/1.94 = 30.52 s
=> Power = Work/time = (20.785*1000)/30.52.......(I multiplied work by 1000 to convert from kJ to J)
=> 681.089 W
=> now 1W = 0.001341 hp
=> Power = 681.089*0.001341 = 0.913335 hp
👍 35 | 👎 -8
Power is simply the total energy used divised by the time.
T = time, X = distance moved, V=Velocity, E=total Energy
P = Power = E.V / X
👍 30 | 👎 -15