Physics Force & Motion BUMHS 2022
PMDC Verified Question 79 of 137
If two equal masses are in motion with same individual speeds, we can conclude that:
A
Their momentums are same
B
Their momentums can be different from each other
C
Their kinetic energies can be different from each other
D
Their total energies are same
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Their momentums can be different from each other
Concept:

Distinguish carefully between scalar quantities (mass, speed, kinetic energy) and vector quantities (velocity, momentum).

Solution:

  • Momentum is a vector: \( \vec{P} = m\vec{v} \). It depends on both mass and the direction of velocity.


  • The prompt says they have the same speed (scalar), but does NOT guarantee they are moving in the same direction.


  • If one moves North and the other South, their momentums are opposite, despite identical speeds and masses.


  • Therefore, their momentums CAN be different.


Why other options are incorrect:

Option A falsely assumes same speed = same direction. Option C is wrong because Kinetic Energy (\( \frac{1}{2}mv^2 \)) is a scalar dependent ONLY on speed and mass, so their K.E. must be exactly identical, never different.

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