# Homework Help: Helicopter accelerates while liftin what are the forces' magnitudes?

1. Oct 14, 2008

### Natali

1. The problem statement, all variables and given/known data
A 7690 kg helicopter accelerates upward at 0.80 m/s2 while lifting a 1260 kg frame at a construction site. (a) What is the lift force exerted by the air on the helicopter rotors? (b) What is the tension in the cable (ignore its mass) that connects the frame to the helicopter? (c) What force does the cable exert on the helicopter?

2. Relevant equations
newtons laws of motion

3. The attempt at a solution
draw free body diagram for both objects. use second law of motion.
what does it mean by "helicopter rotors"? the cable gives tension but it refers to the "force the cable exerts" as something seperate...

2. Oct 14, 2008

### physics girl phd

helicopter rotors (blades) are just providing a lift force (through aerodynamics processes).

The tension in the cable IS the force the cable exerts on the copter.

Don't get bogged down by wording. I like here that you've mentioned drawing two diagrams. Again, the tension links them and the acceleration is not zero, but you can still use the diagrams to get expressions for Fnet... Fnet just isn't zero.