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5.work,energy,power and collision — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics5.work,energy,power and collision1 Mark
MCQ
A $60\; HP$ electric motor lifts an elevator having a maximum total load capacity of $2000\; \mathrm{kg}$. If the frictional force on the elevator is $4000 \;\mathrm{N}$. the speed of the elevator at full load is close to ..............  $\mathrm{m} / \mathrm{s}$

$\left(1 \;\mathrm{HP}=746 \;\mathrm{W}, \mathrm{g}=10\; \mathrm{ms}^{-2}\right)$

  • A
    $1.7$
  • B
    $2$
  • ✓
    $1.9$
  • D
    $1.5$
✓

Answer

Correct option: C.
$1.9$
c
Let elevator is moving upward with constant speed V.
Tension in cable

$\mathrm{T}=2000 \mathrm{g}+\mathrm{f}_{\mathrm{r}}=2000+4000$

$\mathrm{T}=24000 \mathrm{N}$

Power $P=T V$

$\Rightarrow 60 \times 746=(24000) \mathrm{V}$

$\mathrm{V}=\frac{60 \times 746}{24000}=1.865 \approx 1.9 \mathrm{m} / \mathrm{s}$

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