Physics Force & Motion DUHS 2022
PMDC Verified Question 83 of 137
A helicopter of weight 'W' is ascending with zero acceleration. The upward force 'F' on it is:
A
\( F > W \)
B
\( F = \sqrt{W} \)
C
\( F = 0 \)
D
\( F = W \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \( F = W \)
Concept:

According to Newton's Second Law, acceleration is directly proportional to net force. Zero acceleration implies zero net force.

Formula:

$$ \Sigma F = ma $$

$$ F_{up} - F_{down} = m(0) $$

Solution:

  • The upward force is the lift \( F \).


  • The downward force is the weight \( W \).


  • Since acceleration is exactly zero (it is moving at a steady, uniform velocity), the forces must perfectly balance.


  • $$ F - W = 0 \implies F = W $$


Why other options are incorrect:

If \( F > W \), the helicopter would be accelerating upward (speeding up). If \( F < W \), it would be decelerating (slowing down). Zero force implies no lift, meaning it would be in freefall.

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