Question

A rocket with a lift-off mass $2 \times 10^{5}N$kg is blasted upwards with an initial acceleration of $5ms^{- 2}$. The initial thrust of the blast is (Take $g = 10ms^{- 2}$) :

• A. $2 \times 10^{5}N$
• B. $3 \times 10^{5}N$
• C. $4 \times 10^{5}N$
• D. $5 \times 10^{5}N$

Answer 1

Answer: (B)

$3 \times 10^{5}N$

Answer 2

Here $m = 2 \times 10^{4}$kg

Initial acceleration, $a = 5ms^{- 2}$

Initial thrust = upthrust required to impart acceleration a + upthrust required to overcome gravitational pull

}{= (2 \times 10^{4}kg)(5 + 10)ms^{- 2} = 3 \times 10^{5}N}$$