Question

A 10 m high rocket containing liquid fuel of specific gravity 1.2 lifts off at an acceleration of 5 g. The pressure on the bottom plate of the rocket during lift-off is

• A. 6.7 kg/c$m^2$
• B. 7.2 kg/c$m^2$
• C. 8.4 kg/c$m^2$
• D. 8.9 kg/c$m^2$

Answer 1

The correct option is B 7.2 kg/c$m^2$

The height of fuel column, h= 10 m
Pressure at bottom , p= ${\rho }_{fuel}(a+g)h$
where a is the upward acceleration
${\rho }_{fuel}=Specificgravity\times {\rho }_w=1.2\times 10001200kg/m^3\therefore p=1200\times (5g+g)\times 10=1200\times 6\times 10\times 100=7.2\times {10}^{5}N/m^2=7.2kg/c{m}^2$