Physics Work & Energy UHS 2022
PMDC Verified Question 41 of 108
A particle of mass m at rest is acted upon by a force P for time t. Its kinetic energy after time t is:
A
\( P^2t^2/m \)
B
\( P^2t^2/2m \)
C
\( P^2t^2/3m \)
D
\( P^2t^2/4m \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( P^2t^2/2m \)
Concept:

Newton's Second Law and Kinematics can be used to find the final velocity, which is then substituted into the Kinetic Energy equation.

Formula:

$$ a = \frac{F}{m} \quad \text{and} \quad v = u + at \quad \text{and} \quad K.E = \frac{1}{2}mv^2 $$

Solution:

  • Acceleration \( a = \frac{P}{m} \) (where Force is labeled P).


  • Since it starts from rest (\( u = 0 \)), final velocity is \( v = at = \left(\frac{P}{m}\right)t \).


  • Kinetic Energy \( K.E = \frac{1}{2}mv^2 \).


  • Substitute \( v \): \( K.E = \frac{1}{2}m\left(\frac{Pt}{m}\right)^2 = \frac{1}{2}m \left(\frac{P^2t^2}{m^2}\right) \).


  • Simplify to get: \( K.E = \frac{P^2t^2}{2m} \).


Why other options are incorrect:

Option A forgets the \( 1/2 \) factor in the kinetic energy formula. Options C and D introduce incorrect fractional coefficients not present in derivation.

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