Camera drone and speed of air below it

  • Thread starter Thread starter hello478
  • Start date Start date
  • Tags Tags
    Air Drone Speed
Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
Sign up Log in
5 replies · 1K views
hello478
Messages
165
Reaction score
14
Homework Statement
image below
Relevant Equations
f=ma
my answer =
F = 1.6*9.81 - 1.2*9.81 = 3.924 N -> resultant force of the drone moving (weight minus the upward force)
M= 1.2kg , mass of drone
a= 3.31 m/s^2 , acceleration of drone
u=0 m/s , initial speed of drone
t=1s , time
v = 3.27 m/s, final speed of drone
and its not even in the options... 😶

1712081580688.png
 
Physics news on Phys.org
Orodruin said:
It is impossible to follow what you are actually trying to do in your attempt. Please write out units and explain what you are doing in each step.
done
 
hello478 said:
F = 1.6*9.81 - 1.2*9.81
Where does 1.6kg come from? You seem to have added the mass of the drone to the mass of the air it pushes down in one second. In what way do those add? You can't add a mass to a mass per unit time.
If, instead, you had been told it pushes down 1440kg per hour, would you have done 1.2+1440?
 
You have a mass of air, m, accelerated to a velocity, v, in 1 s. What is the force associated with this?
 
Reply
  • Like
Likes   Reactions: Lnewqban
hello478 said:
my answer =
F = 1.6*9.81 - 1.2*9.81 = 3.924 N -> resultant force of the drone moving (weight minus the upward force)
Note that the hovering drone is not moving in any direction.
Therefore, the resultant force in any direction must be null or zero.

The mass of air that each propeller accelerates downwards (from zero to the value of V that the problem is asking about), generates an upwards force.

Still, the drone does not move, because all the forces acting on it balance each other.

Hint:
Drones depart from the balanced condition of hovering and move upwards when the pilot simultaneously increases the rotational speed of all the propellers (via manipulation of the left lever of the remote control).

Could you tell what happens to the individual mass of air, its acceleration, and induced force in that case?