A body of mass 5, kg starts from origin with an initial velocity overrightarrow {u,} , = ,30hat{i} +

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4-1.Newton's Laws of Motion

easy

A body of mass $5\, kg$ starts from the origin with an initial velocity $\overrightarrow {u\,} \, = \,30\hat i + 40\hat j\,m{s^{ - 1}}$. If a constant force $\overrightarrow {F\,} = - (\hat i + 5\hat j)N$ acts on the body, the time in which the y-component of the velocity becomes zero is ......... $\sec$

A

$5$

B

$20$

C

$40$

D

$80$

Solution

(c) ${u_y} = 40\,m/s$, ${F_y} = – 5N$, $m = 5\,kg$.

So ${a_y} = \frac{{{F_y}}}{m} = – 1\,m/{s^2}$ (As $v = u + at$)

${v_y} = 40 – 1 \times t = 0$ $⇒$ $t = 40\,\sec $.

Standard 11

Physics

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