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Work, Energy, and Power — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysicsWork, Energy, and Power1 Mark
MCQ
A particle is pushed by forces $2\hat{\text{i}}+3\hat{\text{j}}-2\hat{\text{k}}$ and $5\hat{\text{i}}+\hat{\text{j}}-2\hat{\text{k}}$ simultaneously and it is displaced from point $\hat{\text{i}}+\hat{\text{j}}+\hat{\text{k}}$ to point $2\hat{\text{i}}-\hat{\text{j}}-2\hat{\text{k}}$. The work done is:
  • A
    7 units.
  • B
    -7 units.
  • C
    10 units.
  • D
    -10 units.
✓

Answer

  1. -7 units.

Explanation:

Net force, $=2\hat{\text{i}}+3\hat{\text{j}}-2\hat{\text{k}+}5\hat{\text{i}}-\hat{\text{j}}-3\hat{\text{k}}$

$=7\hat{\text{i}}+2\hat{\text{j}}-5\hat{\text{k}}$

Diolacement, $\text{d}=2\hat{\text{i}}-\hat{\text{j}}+3\hat{\text{k}-}\hat{\text{i}}-\hat{\text{j}}-\hat{\text{k}}$

$=\hat{\text{i}}-2\hat{\text{j}}+2\hat{\text{k}}$

Work done $=\text{F}.\text{d}=(7\hat{\text{i}}+2\hat{\text{j}}-5\hat{\text{k}}).(\hat{\text{i}}-2\hat{\text{j}}+2\hat{\text{k}})$

$=7-4-10=-7\text{ units}$.

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