Respuesta :
Answer:
Explanation:
In absence of friction
Work done by force is given by change in kinetic energy of box
According work Energy theorem change in kinetic Energy of object is equal to work done by all the forces
[tex]W_1=\frac{1}{2}mv^2-0[/tex]
[tex]W_1=\frac{1}{2}mv^2[/tex]
where m=mass of object
[tex]W_2=\frac{1}{2}m(2v)^2-\frac{1}{2}mv^2[/tex]
[tex]W_2=\frac{3}{2}mv^2[/tex]
[tex]\frac{W_2}{W_1}=\frac{\frac{3}{2}mv^2}{\frac{1}{2}mv^2}[/tex]
[tex]W_2>W_1[/tex]
so work done in second case is three times of first case
(b)In Presence of friction
[tex]W_f+W_1=\frac{1}{2}mv^2[/tex]
suppose [tex]f_r[/tex] is the friction force and d is the displacement
so [tex]W_f=f_r\cdot d\cos 180[/tex]
[tex]W_f=-f_r\cdot d[/tex]
[tex]W_1=\frac{1}{2}mv^2+f_r\cdot d[/tex]
for second case when speed increases v to 2v
[tex]W_2=\frac{3}{2}mv^2+f_r\cdot d[/tex]
thus [tex]W_2>W_1[/tex] when friction is present
The work done to accelerate the box from zero is lesser than the work done to accelerate the box from velocity [tex]v[/tex].
From Work- energy theorem,
Work can be defined as the change in the kinetic energy of the object.
So,
In the first Scenario,
[tex]W_1 = \dfrac 12 mv^2- 0\\\\W_1 = \dfrac 12 mv^2[/tex]
In the second scenario,
[tex]W_2 = \dfrac 12 m(2v^2) -\dfrac 12 mv^2\\\\W_2 = \dfrac 32 mv^2[/tex]
Now compare both scenarios,
[tex]\dfrac {W_1}{W_2}=\dfrac{ \dfrac 32 mv^2}{\dfrac12 mv^2}[/tex]
So, [tex]W_1 <W_2[/tex]
Therefore, the work done to accelerate the box from zero is lesser than the work done to accelerate the box from velocity [tex]v[/tex].
Learn more about Work- energy theorem,
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