Physics Work & Energy MDCAT 2019
PMDC Verified Question 81 of 108
Which of the following statement shows that no work is done?
A
Pushing a car to start it moving
B
Lifting the weights
C
Writing an essay on a page
D
The moon orbiting the earths
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: The moon orbiting the earths
Concept:

In physics, mechanical work is zero if the force acts perpendicularly to the direction of motion at all times.

Formula:

$$ W = Fd \cos(90^{\circ}) = 0 $$

Solution:

  • For a moon orbiting Earth in a circular path, the gravitational force provides centripetal force, pointing towards Earth's center.


  • The velocity (and instantaneous displacement) is tangential, forming a 90° angle with the force.


  • Therefore, \( \cos(90^{\circ}) = 0 \), so no work is done.


Why other options are incorrect:

Pushing a car and lifting weights involve forces applied in the same direction as displacement, doing positive work. Writing involves frictional forces and micro-displacements, doing work.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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