Apparent weight in free fall When a body falls freely under the action of gravity (e.g., in an ideal freely falling elevator), what happens to its apparent weight?
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Amaximum weight
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Bminimum weight
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Cno weight
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Dno effect on its weight
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Eweight increases by g/2 factor
Answer
Correct Answer: no weight
Explanation
Introduction / Context:Apparent weight is the normal reaction measured by a scale. In free fall, many systems experience weightlessness, a key idea in astronautics and drop-tower experiments. Distinguishing true gravitational weight from the apparent weight is essential.
Given Data / Assumptions:
- Body is in ideal free fall under gravity alone (acceleration g downward).
- No air resistance; we evaluate the scale reading or normal reaction.
- “Weight” in this context refers to apparent weight (scale reading).
Concept / Approach:
A scale measures the normal reaction R. For a body of mass m on a scale in an elevator with acceleration a downward, R = m(g − a). In free fall, a = g, hence R = 0. The gravitational force mg still acts, but the apparent weight (what the scale reads) is zero, producing weightlessness.
Step-by-Step Solution:
Let true weight W_true = m * g (constant).For elevator acceleration a downward: R = m(g − a).In free fall: a = g ⇒ R = 0.Thus, apparent weight (scale reading) is zero; the body experiences weightlessness.Verification / Alternative check:
Free-body diagram shows only gravity acting, with the supporting contact lost; without a normal force, scales read zero. Astronaut training aircraft simulate brief weightlessness during parabolic flight for the same reason (effective acceleration equals g downward).
Why Other Options Are Wrong:
(a) and (b) imply extremes of apparent weight but not zero. (d) claims no change, which contradicts the zero-reaction result. (e) is physically meaningless for weight in this scenario.
Common Pitfalls:
Confusing true weight mg (unchanged) with apparent weight (scale reading); thinking zero gravity is required for weightlessness—it is sufficient that support force is zero.
Final Answer:
no weight