A man stands in a lift that is accelerating vertically downwards. Which statement describes the force exerted by the man on the floor?
Correct answer: D. It is less than the weight of the man.
- A. It is equal to the weight of the man.
- B. It is greater than the force exerted by the floor on the man.
- C. It is less than the force exerted by the floor on the man.
- D. It is less than the weight of the man.
Explanation
As the lift is accelerating vertically downward so (g-a). The apparent weight of a man would become less than the actual weight. F=W-Rma=mg-RR=mg-maR= m(g-a)If the lift would be moving upward then (g+a), both g and acceleration would be parallel F=R-Wma=R-mgma+mg=RR=m(a+g)In the case of acceleration, the weight and the exerted force can't be equal. The weight of man and exerted force will be equal if the lift is at rest or moving with constant speed. The floor would apply a force on a man equal to the weight of a man.
This question appeared on the ETEA MDCAT 2018 paper, which you can sit online with every answer explained.
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