Question

A rocket of mass $5700kg$ ejects mass at a constant rate of $15kg/s$ with constant speed of $12km/s$. The acceleration of the rocket $1$ minute after the blast is ($g=10m/s^2$)

• A. $34.9m/s^2$
• B. $27.5m/s^2$
• C. $3.50m/s^2$
• D. $13.5m/s^2$

Answer 1

The correct option is B $27.5m/s^2$

Mass of rocket after 1 minute $M=5700-15\times 60=4800kg$

Upthrust force $F_u=v\frac{dm}{dt}=12000\times 15=180000N$

So, acceleration $a=\frac{F_u-Mg}{M}$

Or $a=\frac{180000-4800\times 10}{4800}=27.5m/s^2$