Question

Two opposite charge particles under mutual force of attraction are given uniform initial velocity of same magnitude in opposite direction. They lose $220\text{J}$ of their $K.E$ after travelling $2\text{m}$ distance. Calculate the work done by internal force

• A. Zero
• B. $-220\text{J}$
• C. $+220\text{J}$
• D. $110\text{J}$

Answer 1

The correct option is B $-220\text{J}$


Since they are under force of attraction and displacement is given in opposite direction (They are made to separate).
Therefore work done will be $-ve$ and its magnitude will be the change in kinetic energy.

$\therefore$ Work done by internal force $=$ change in the $K.E$
$W=-220J$,
Here we get $-ve$ the direction of force of attraction is opposite to the direction of displacement.

Hence option B is the correct answer