Calculating Lift Force for a Helicopter and Car System

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Homework Help Overview

The discussion revolves around calculating the lift force exerted by air on a helicopter that is lifting a car while accelerating upward. The problem involves understanding the forces acting on a combined mass system, including the helicopter and the car, and applying Newton's laws of motion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants explore the application of F=ma to a system of combined masses, question the necessity of considering additional forces such as tension, and discuss the importance of free body diagrams in visualizing forces.

Discussion Status

The discussion is ongoing with participants questioning assumptions about the forces involved and the calculations required. Some guidance has been offered regarding the conversion of units and the grouping of masses, but there is no explicit consensus on the final approach to calculating the lift force.

Contextual Notes

Participants are navigating the challenge of combining different units (pounds to kilograms) and understanding the implications of various forces acting on the system, including gravitational force and tension.

MorganJ
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Homework Statement



A 13,000-kg helicopter accelerates upward at 0.37 m/s^2 while lifting a 2000 pound car. To the nearest Newton, what is the lift force exerted by the air on the rotors?

Homework Equations


I thought since the problem is dealing with forces, I would use F=ma but that wouldn't be the only equation I would use. I know I am dealing with two masses so I don't know how to arrive at the answer.
 
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You can still use F = ma. In fact you should. The masses move as one, so you can pretend they are a single mass. Don't forget to convert the weight of the car from pounds to mass in kilograms.
 
Okay so do I group the helicopter and the car as one by adding the two masses together? And if so, how do I get the lift force? I know it cannot just be by doing F=ma.
 
MorganJ said:
Okay so do I group the helicopter and the car as one by adding the two masses together? And if so, how do I get the lift force? I know it cannot just be by doing F=ma.

Yes, you group the helicopter and the car as one. How do you know "it cannot just be by doing F = ma?" Draw a free body diagram and put in all the forces. The force exerted on the system by the air is only one of them.
 
it would just be (15000)(0.37), that would be only 5550 N. Wouldn't the number be a bit bigger than that? Wouldn't tension be involved?
 
First off what does 15000 represent? Let me repeat what I said in post#2. "Don't forget to convert the weight of the car from pounds to mass in kilograms."

Secondly, did you draw a free body diagram? What does multiplying the mass of the (helicopter plus car) system by the acceleration give you? Hint: It is not the force exerted by the air. What force is it?
 
Oh, I see! So 2000 lbs. roughly is about 909.1 kg. So 13,000+909.1= 13909.1 kg. (13909.1)(0.37)=5146.367 N. Wouldn't the force be the force of gravity?
 
Ok I found the answer. Thank you for your help.
 
No. The force of gravity is mg. Read up on Newton's Second Law. What does F on the left side of the equaiton stand for?
 
  • #10
I am glad you found the answer.
 

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