GRE Physics GR1777, Problem 019 Solution

GRE Physics GR 1777 Problem Solution

019. Classical Mechanics (Work-Energy Principle)

Solution

From the work-energy theorem,

$latex W = \\Delta K = \\frac{1}{2} mv_f^2 – \\frac{1}{2} mv_i^2$
 

Since the work done by the box is

$latex W = F \\cdot d = F \\cdot (5 m)$
and the change of the kinetic energy is

$latex \\frac{1}{2} mv_f^2 – \\frac{1}{2} mv_i^2 = \\frac{1}{2} (10 kg) \\cdot [ (2 m/s)^2 – (1 m/s)^2] = 15 kg \\cdot m^2/s^2 $
 

Therefore, The force is

$latex F = 3 kg \\cdot m/s^2 = 3N $

Answer

(C) 3N

Reference

https://en.wikipedia.org/wiki/Work_(physics)#Work–energy_principle

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