Calculating Lift Force for a Helicopter and Car System

In summary, the conversation discusses how to calculate the lift force exerted by the air on a helicopter lifting a car while accelerating upward. The equation F=ma is used, with the masses of the helicopter and car combined as one. The weight of the car must be converted from pounds to kilograms. A free body diagram is recommended to understand the forces involved. The final answer is found to be 5146.367 Newtons.
  • #1
MorganJ
32
0

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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  • #2
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.
 
  • #3
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.
 
  • #4
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.
 
  • #5
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?
 
  • #6
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?
 
  • #7
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?
 
  • #8
Ok I found the answer. Thank you for your help.
 
  • #9
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.
 

FAQ: Calculating Lift Force for a Helicopter and Car System

What is lift force?

Lift force is a force that acts on a body in a fluid (such as air or water) in a direction perpendicular to the fluid's flow. It is responsible for the upward movement of an object, such as an airplane, in the fluid.

How is lift force created?

Lift force is created by the difference in pressure above and below an object as it moves through a fluid. This difference in pressure is caused by the shape of the object and the way it interacts with the fluid.

What factors affect lift force?

The factors that affect lift force include the shape and size of the object, the speed at which it is moving through the fluid, the density and viscosity of the fluid, and the angle of attack (the angle between the object's surface and the direction of the fluid flow).

How is lift force related to two masses?

In the context of lift force, two masses refer to the weight of an object and the weight of the fluid it displaces. When an object is placed in a fluid, the fluid exerts an upward force on the object equal to the weight of the fluid it displaces. This is known as Archimedes' principle and is related to lift force because it affects the overall buoyancy of the object in the fluid.

How is lift force measured?

Lift force can be measured using a variety of methods, such as wind tunnel testing, computational fluid dynamics, and strain gauge measurements. These methods involve measuring the forces acting on an object as it moves through a fluid and analyzing the data to determine the lift force.

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