Question

A rocket with a lift-off mass $3.5\times {10}^{4}kg$ is blasted upwards with an initial acceleration of $10m/s^2$. The initial thrust of the blast is:

• A. $3.5\times {10}^{5}N$
• B. $7.0\times {10}^{5}N$
• C. $1.40\times {10}^{5}N$
• D. $1.75\times {10}^{5}N$

Answer 1

The correct option is D $1.75\times {10}^{5}N$

$mg$ force due to gravity acts on the rocket in downward direction, and T thrust acts in upward direction.
Net Force $F=T-mg$ in the upward direction
given that net acceleration is $10m/s^2$ in upward direction.
$\therefore T-mg=ma⟹T=m(g+a)=3.5\times {10}^4\times (10+10)=7.0\times {10}^{5}N$