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4-1.Newton's Laws of Motion
normal
A rocket with a lift-off mass $2\times10^4\, kg$ is blasted upwards with an intial acceleration of $5\, m\, s^{-2}$. The initial thrust of the blast is (Take $g = 10\, m\, s^{-2}$)
A
$2\times10^5\, N$
B
$3\times10^5\, N$
C
$4\times10^5\, N$
D
$5\times10^5\, N$
Solution
Here, $\mathrm{m}=2 \times 10^{4} \mathrm{kg}$
Initial acceleration, $a=5 \mathrm{m} \mathrm{s}^{-2}$
Initial thrust $=$ upthrust required to impart
acceleration a $+$ upthrust required to overcome
gravitational pull
$\therefore \mathrm{F}=\mathrm{m}(\mathrm{a}+\mathrm{g})$
$=\left(2 \times 10^{4} \mathrm{kg}\right)(5+10) \mathrm{m} \mathrm{s}^{-2}=3 \times 10^{5} \mathrm{N}$
Standard 11
Physics
