Question

A constant retarding force of $50 \,N$ is applied to a body of mass $10\, kg$ moving initially with a speed of $10\, m\, s^{-1}.$ The body comes to rest after

• A. $2\, s$
• B. $4\, s$
• C. $6 \,s$
• D. $8 \,s$

Answer 1

Answer: (A)

$2\, s$

Answer 2

Here, $F=-50\, N$ ($-ve$ sign for retardation) $m=10 \,kg,$ $u=10 m \, s^{-1},$ $v=0$ As $F=m a$ $\quad\quad$ $\therefore\quad$ $a=\frac{F}{m}$ $=\frac{-50 N}{10 \, kg}$ $=-5 \, m \, s^{-2}$ using $v=u+at$ $\quad\quad$ $\therefore\quad$ $t=\frac{v-u}{a}$ $=\frac{0-10 \,m \,s^{-1}}{-5\, m \,s^{-2}}$ $=2\, s$