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

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Homework Help Overview

The discussion revolves around determining the number of prime movers required to pull a crane weighing 2000 tonnes at a velocity of 10 m/min. The problem involves considerations of power, friction, and acceleration.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the relationship between power, force, and velocity, with one participant calculating the required power based on mass and friction. Others question the assumptions regarding acceleration and the conversion of units, particularly regarding friction forces.

Discussion Status

The discussion is ongoing, with participants providing clarifications and exploring different aspects of the problem. Some guidance has been offered regarding the need to consider both the power required to accelerate the crane and the power needed to maintain its velocity against friction.

Contextual Notes

There are uncertainties regarding the assumptions made about the crane's acceleration and the nature of friction forces. Participants are also discussing the need for unit conversions and the implications of these on the calculations.

ainaz89
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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