Question

A particle has an initial velocity $3\hat{i}+4\hat{j}$ and an acceleration of $0.4\hat{i}+0.3\hat{j}$. Its speed after $10\, s$ is

• A. $10$ units
• B. $7\sqrt{2}$ units
• C. $7$ units
• D. $8.5$ units

Answer 1

Answer: (B)

$7\sqrt{2}$ units

Answer 2

$\overrightarrow{u}=3\hat{i}+4\hat{j} ; \overrightarrow{a}=0.4\hat{i}+0.3\hat{j}$ $\overrightarrow{u}=\overrightarrow{u}+\overrightarrow{a}t$ $=3\hat{i}+4\hat{j}+\left(0.4\hat{i}+0.3\hat{j}\right)10=3\hat{i}+\hat{j}+4\hat{i}+3\hat{j}=7\hat{i}+7\hat{j}$ Speed is $\sqrt{7^{2}+7^{2}}=7\sqrt{2}$ units