A circular disc has a mass of 1 kg and radius 40 cm . It is rotating about an axis passing through its centre and perpendicular to its plane with speed of 10 rev / s. The work done in joules in stopping it would be (π2 ≈ 10) :

Question

A circular disc has a mass of 1 kg and radius 40 cm . It is rotating about an axis passing through its centre and perpendicular to its plane with speed of 10 rev / s. The work done in joules in stopping it would be (π2 ≈ 10) : (A) 4 (B) 47.5 (C) 79 (D) 160

Tardigrade Admin · Accepted Answer

<img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/a13c217aa1ad70ec4d48412509669b16-.png" /> W =Δ K W =(1/2) I ω2 =(1/2) ( MR 2/2) ×(2 π f )2 =(M R2/4) × 4 π2 ×(10)2 =1 ×(0.4)2 × 10 × 100 ≃ 160

Q. A circular disc has a mass of $1 k g$ and radius $40 c m .$ It is rotating about an axis passing through its centre and perpendicular to its plane with speed of $10 re v / s$ . The work done in joules in stopping it would be $(π^{2} \approx 10)$ :

$4$

$47.5$

$79$

$160$

$W = Δ K$
$W = \frac{1}{2} I ω^{2}$
$= \frac{1}{2} \frac{M R ^{2}}{2} \times (2 π f)^{2}$
$= \frac{M R ^{2}}{4} \times 4 π^{2} \times (10)^{2}$
$= 1 \times (0.4)^{2} \times 10 \times 100$
$≃ 160$

Q. A circular disc has a mass of 1kg and radius 40cm. It is rotating about an axis passing through its centre and perpendicular to its plane with speed of 10rev/s. The work done in joules in stopping it would be (π2≈10) :

4

47.5

79

160

W=ΔK W=21​Iω2 =21​2MR2​×(2πf)2 =4MR2​×4π2×(10)2 =1×(0.4)2×10×100 ≃160

Q. A circular disc has a mass of $1 k g$ and radius $40 c m .$ It is rotating about an axis passing through its centre and perpendicular to its plane with speed of $10 re v / s$ . The work done in joules in stopping it would be $(π^{2} \approx 10)$ :

$4$

$47.5$

$79$

$160$

$W = Δ K$
$W = \frac{1}{2} I ω^{2}$
$= \frac{1}{2} \frac{M R ^{2}}{2} \times (2 π f)^{2}$
$= \frac{M R ^{2}}{4} \times 4 π^{2} \times (10)^{2}$
$= 1 \times (0.4)^{2} \times 10 \times 100$
$≃ 160$