Physics Work & Energy PMDC 2020
PMDC Verified Question 75 of 108
A 1.75 m heighted weight-lifter raises weights with a mass of 50 kg to a height of .5m above his head. How much work is being done by him? (\( g=10 \text{ ms}^{-2} \))
A
2125J
B
2500 J
C
50J
D
1125 J
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 1125 J
Concept:

Work done against gravity is the product of weight (mg) and the total vertical displacement from the ground.

Formula:

$$ W = mgh $$

Solution:

  • Mass (\( m \)) = 50 kg


  • Total vertical height from ground (\( h \)) = Lifter's height + extra height = 1.75 + 0.5 = 2.25 m


  • \( g = 10 \text{ m/s}^2 \)


  • \( W = 50 \times 10 \times 2.25 = 500 \times 2.25 = 1125 \text{ J} \)


Why other options are incorrect:

Using only the lifter's height gives 875 J. Using only the height above the head gives 250 J. You must use the total vertical lift distance from rest.

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