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Rotational Motion question

2021 · 17 Mar · Shift 1 · Q63
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  5. /2021 · 17 Mar · Shift 1 · Q63

Rotational Motion question

2021 · 17 Mar · Shift 1 · Q63

JEE MainPhysicsRotational MotionNumerical+4 / −1
The angular speed of truck wheel is increased from 900 rpm to 2460 rpm in 26 seconds. The number of revolutions by the truck engine during this time is ‾\underline{\hspace{2cm}}​. (Assuming the acceleration to be uniform).
Numerical answer
View written solutionFree

Correct answer: 728

  1. Given data
  • Initial angular speed of wheel: 900 rpm900\ \text{rpm}900 rpm
  • Final angular speed of wheel: 2460 rpm2460\ \text{rpm}2460 rpm
  • Time taken: 26 s26\ \text{s}26 s
  • Angular acceleration is uniform.

We need the number of revolutions during this interval.

  1. Use average angular speed

For uniform angular acceleration,

ωavg=ωi+ωf2\omega_{\text{avg}}=\frac{\omega_i+\omega_f}{2}ωavg​=2ωi​+ωf​​

So,

ωavg=900+24602=33602=1680 rpm\omega_{\text{avg}}=\frac{900+2460}{2}=\frac{3360}{2}=1680\ \text{rpm}ωavg​=2900+2460​=23360​=1680 rpm

  1. Convert time into minutes

Since speed is in rpm, convert 262626 s into minutes:

t=2660=1330 mint=\frac{26}{60}=\frac{13}{30}\ \text{min}t=6026​=3013​ min

  1. Find number of revolutions

Number of revolutions = average rpm ×\times× time in minutes:

N=1680×1330N=1680\times \frac{13}{30}N=1680×3013​

N=56×13=728N=56\times 13=728N=56×13=728

  1. Final answer

728\boxed{728}728​

  1. Comparison with stored correct answer

Stored correct answer = 728728728

Our derived answer also is 728728728, so they agree.

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