# A disc of radius 2 m and mass 100 Kg rolls on a horizontal floor . Its center of mass has speed of 20 cm/s . How much work is needed to stop it ? Option 1)3 J Option 2)30 Kj Option 3)2 J Option 4)1 J

$W = \Delta KE \\\\ = \frac{1}{2} IW^2 + \frac{1}{2} mV^2 \\\\ = \frac{1}{2} \times \frac{1}{2} mR^2 \omega ^ 2 + \frac{1}{2} m V^2 \\\\ (use \ V= \omega R ) \\\\ = \frac{1}{4} mV^2 + \frac{1}{2}m V^2 \\\\ W = \frac{3}{4} mV^2 \\\\ W = \frac{3}{4} \times 100 \times \frac{20 \times 20 }{100 \times 100} \\\\ W = 3 J$

Option 1)

3 J

Option 2)

30 Kj

Option 3)

2 J

Option 4)

1 J

Exams
Articles
Questions