Question

A block of mass 1 kg slides down a curved track which forms one quadrant of a circle of radius 1 m as shown in figure. The speed of block at the bottom of the track is $v=2m{s}^{-1}$. The work done by the force of figure is

• A. +4J
• B. -4J
• C. -8J
• D. +8J

Answer 1

Answer: (C)

-8J

Work done by friction + work done by gravity

$=$ change in kinetic energy

$=\frac{1}{2}\times (2^2-0^2)$

$\frac{1}{2}\times 4=2$

work done by gravity $=1\times 10\times 10$

$=10$

-ve because 'f' and displacement are opposite

$\therefore$ work done by friction $=-10+2$

$=-8J$