How many prime mover is needed to pull the crane with velocity 10m/min?

AI Thread Summary
To determine the number of prime movers needed to pull a 2000-tonne crane at a velocity of 10 m/min, calculations show that the required power is approximately 3,135,276 watts. Given that each prime mover provides 164,120 watts, the initial calculation suggests 19 units are necessary. However, clarification is sought on whether the crane's acceleration and friction forces are correctly accounted for, as friction should be expressed in Newtons rather than tonnes. The discussion emphasizes the need to analyze both the power required for acceleration and the power needed to maintain constant velocity, with a focus on overcoming friction. The conclusion indicates that the calculations and assumptions may need to be reassessed to align with expected outcomes of fewer than 10 prime movers.
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Homework Statement



prime mover = 220 hp
crane = 2000 tonne
velocity crane = 10m/min = 0.17m/sec
acceleration crane = 0.017m/sec
every 100 tonne = 6 tonne of friction

1hp = 726 W
1 tonne = 1000 kg

Homework Equations



how many prime mover are needed to pull the crane?prime mover 220 hp = 164120W

for every 100 tonne = 6 tonne of friction
2000tonne = 120 tonne of friction

m = 2000tonne - 120 tonne = 1880 tonne

P = F*v
= mg * v
= (1880*1000)(9.81)*(0.17)
= 3135276W

so, total of PM = 3135276/164120
= 19 units.

the answer should be less than 10 units.
 
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I need some clarification for this problem. Can I assume that the crane accelerates from rest to a final velocity of .17 m/s at an acceleration of .017 m/s^2? Friction forces are in Newtons not Kg (or tonne). Is 120 tonne friction 120,000 Kg * 9.8 M/s^2= 1.18 x 10^6 Newtons? 1 prime mover unit is 164,120 watts?
 
RTW69: yes..the acceleration of the crane is 0.017m/s^2.and u can change the parameters into SI unit.as i calculated, the prime mover power is 164120 watts.
 
OK, there are two parts to this problem. Part 1 is how much power is required to get the crane from rest to a final velocity given the acceleration. You need to do a free body diagram oft he accelerating crane, sum of the forces in x-direction=M*a. Use your one-dimensional motion equations to find distance and time for crane to reach final velocity. Power= F*D/t

The second part of the problem is how much power is required to keep the crane moving at final velocity. There is no acceleration so sum of forces in x-direction=0. The motor just needs to overcome the friction forces. Power=F*Vel. Which power requirement is larger, part 1 or part 2? convert larger to power units.

Your P=F*V equation is incorrect
 

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