# Determining Tension & Lift Force for Helicopter & Truck

In summary, the conversation discusses a problem where a 15000-kg helicopter is lowering a 4000-kg truck at a constant rate of 15.0 m/s. The truck, helicopter, and cable need to be slowed to 5.00 m/s in the next 50.0 m of descent to prevent damage to the truck. The tension in the cable and lift force of the helicopter blades need to be determined. The solution involves isolating the truck and helicopter separately and considering the forces acting on each. The tension in the cable is the same everywhere and the gravity vector should be consistent in both halves of the problem.

## Homework Statement

A 15000-kg helicopter is lowering a 4000-kg truck by a cable of fixed length. The truck, helicopter, and cable are descending at 15.0 m/s and must be slowed to 5.00 m/s in the next 50.0 m of descent to prevent damaging the truck. Assume a constant rate of slowing.

Determine the tension in the cable.

Determine the lift force of the helicopter blades

F=ma

## The Attempt at a Solution

dont have answers but attempt was to isolate the system of truck
MG-FT=ma
4000*9.8-ft=4000*-2
ft=48000?

force of lift
LF-mg+mg =ma
LF-15000(9.8)+4000(9.8)=15000+4000(-2)
LF=152000

You isolated the truck but you didn't isolate the helicopter?

Last edited:
why do i need to isolate the helicopter to find the lift i used the entire system

Yes, you're absolutely right. Just fix your signs then.

ohh u mean my 9.8 should be negative lol my bad

No, you used +ve for the truck and -ve for the helicopter.

You have your gravity vector pointing in two different directions.

Also, the tension in the cable is the same everywhere, draw a FBD and cut the problem into two halves. In the top half only consider the helicopter, in the bottom half only consider the truck.

## 1. How is tension calculated for a helicopter?

The tension on a helicopter is calculated by taking into account the weight of the helicopter, the lift force generated by the rotors, and any external forces acting on the helicopter. These forces are then balanced to determine the tension on the helicopter's cables or rotor blades.

## 2. What factors affect the lift force of a helicopter?

The lift force of a helicopter is affected by several factors, including the size and shape of the rotor blades, the angle of attack, air density, and airspeed. Additionally, the weight and distribution of weight on the helicopter can also affect the lift force.

## 3. How is lift force different for a helicopter and a truck?

The lift force for a helicopter is generated by the rotation of the rotor blades, while the lift force for a truck is generated by the upward force of the air on the truck's body as it moves forward. This is why helicopters are able to hover in place, while trucks cannot.

## 4. What is the relationship between lift force and tension in a helicopter?

The lift force and tension in a helicopter are directly proportional. As the lift force increases, so does the tension on the helicopter's cables or rotor blades. This is because the tension is what allows the helicopter to stay in the air and counteract the force of gravity.

## 5. How does air density affect tension and lift force in a helicopter?

Air density plays a significant role in determining the tension and lift force for a helicopter. Higher air density means there is more air for the rotor blades to push against, resulting in a greater lift force and therefore a higher tension on the helicopter's cables or rotor blades. Conversely, lower air density will result in a lower lift force and tension.

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