Question

A body is moving under the action of two forces $\vec{F}_{1}$ $=2 \hat{i}$ $-5 \hat{j} ;$ $\vec{F}_{2}$ $=3 \hat{i}$ $-4 \hat{j}.$ Its velocity will become uniform under a third force $\vec{F}_{3}$ given by

• A. $5 \hat{i}$ $-\hat{j}$
• B. $-5 \hat{i}$ $-\hat{j}$
• C. $5 \hat{i}$ $+\hat{j}$
• D. $-5 \hat{i}$ $+9 \hat{j}$

Answer 1

Answer: (D)

$-5 \hat{i}$ $+9 \hat{j}$

Answer 2

For uniform velocity, acceleration is zero. Hence resultant force will be zero. $\therefore\quad$ $\vec{F}_{1}$ $+\vec{F}_{2}$ $+\vec{F}_{3}=0$ $\left(2\hat{i}-5\hat{j}\right)$ $+\left(3 \hat{i}-4\hat{j}\right)$ $+\vec{F}_{3}=0$ or $\vec{F}_{3}$ $=\left(-5\hat{i}+9 \hat{j}\right)$