Question

If the toy helicopter weighs 115 N and is hovering motionless in the air, which of these options MOST accurately describes the force that the helicopter's propeller must exert?

Answer 1

If the helicopter is not moving, then it is not being accelerated.

By second Newton's law we have that:

F = m*a

Force equals mass times acceleration.

Then if we do not have acceleration, we have:

F = m*a = m*0 = 0.

Then the total force must be zero.

So if the gravitational force (pulling down) is 115N, then the force of the propeller must be such that:

Total force = F - 115N = 0

F = 115N

The force of the propeller must be also of 115N, but in the opposite direction.