Question

The net force on a rocket with a weight of $1.5\times {10}^{4}N$ is $2.4\times {10}^{4}N$. About how much time is needed to increase the rocket's speed from $12m/s$ to $36m/s$ near the surface of the Earth at take off? (Take $g=10m/s^2$)

• A. $15s$
• B. $0.78s$
• C. $1.5s$
• D. $3.8s$

Answer 1

The correct option is C $1.5s$

Weight of the rocket $=1.5\times {10}^{4}N$

Weight = mass $\times$ gravitational acceleration
$\therefore$ Mass of the rocket $=\frac{Weight}{gravitationalacceleration}=\frac{1.5\times {10}^4}{10}=1.5\times {10}^{3}kg$

According to Newton's second law of motion,

$F_{net}=mass\times acceleration$
Acceleration of the rocket $=\frac{Netforce}{mass}=\frac{2.4\times {10}^4}{1.5\times {10}^3}=16m{s}^{-2}$
Given:

$v=36m/s$

$u=12m/s$

$a=16m/s^2$

Using the equation of motion: $v=u+at$
$t=\frac{36-12}{16}=1.5sec$