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Suppose you are pushing a 3 kg box with a force of 25 N (directed parallel to the ground) over a distance of 15 m. Afterward, the box (initially at rest) is traveling at a speed of 6 m/s. How much work (in Joules) did friction do in this process

Sagot :

Answer: 321 J

Explanation:

Given

Mass of the box [tex]m=3\ kg[/tex]

Force applied is [tex]F=25\ N[/tex]

Displacement of the box is [tex]s=15\ m[/tex]

Velocity acquired by the box is [tex]v=6\ m/s[/tex]

acceleration associated with it is [tex]a=\dfrac{F}{m}[/tex]

[tex]\Rightarrow a=\dfrac{25}{3}\ m/s^2[/tex]

Work done by force is [tex]W=F\cdot s[/tex]

[tex]W=25\times 15\\W=375\ J[/tex]

change in kinetic energy is [tex]\Delta K[/tex]

[tex]\Rightarrow \Delta K=\dfrac{1}{2}m(v^2-0)\\\\\Rightarrow \Delta K=\dfrac{1}{2}\times 3\times 6^2\\\\\Rightarrow \Delta K=\dfrac{1}{2}\times 3\times 36\\\\\Rightarrow \Delta K=54\ J[/tex]

According to work-energy theorem, work done by all the forces is equal to the change in the kinetic energy

[tex]\Rightarrow W+W_f=\Delta K\quad [W_f=\text{Work done by friction}]\\\\\Rightarrow 375+W_f=54\\\Rightarrow W_f=-321\ J[/tex]

Therefore, the magnitude of work done by friction is [tex]321\ J[/tex]