Rajasthan BoardEnglish MediumSTD 9ScienceWork And Energy1 Mark
Question
In case of negative work the angle between the force and displacement is:
✓
Answer
180°.
Explanation:
Work done W = F.d $\cos\theta$
$\therefore$ Work done at $\theta=0^\circ,\ \text{W}=\text{F.d}\ \cos0^\circ$ $(\therefore\cos0^\circ=1)$
$\Rightarrow$ W = F.d
For angle $\theta=0^\circ,$
Work done Is positive, so it is not true.
We know that work done, W = F.d $\cos\theta$
$\text{W}=\text{F.d}\ \cos45^\circ$ $\Big(\because\cos45^\circ=\frac{1}{\sqrt{2}}\Big)$
$\text{W}=\frac{\text{F.d}}{\sqrt{2}}$
For angle $0=45^\circ,$
work done is positive, so it is not true.
We know that work done, W = d $\cos\theta$
Work done at $\theta=90^\circ,$ W = F.d $\cos90^\circ$ $(\therefore\cos90^\circ=0)$
W = 0
So, it in not true.
Work done at $\theta=180^\circ,\ \text{W}=\text{F.d}\ \cos\theta\ \ (\therefore\cos180^\circ=-1)$
W = -F.d
For negative work, the angle between the force and displacement should be 180°.
(i.e, force and displacement are anti parallel to each other) So, it is true.
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