Question

A rocket of mass $3\times {10}^6$ kg takes off from a launching pad and acquires a vertical velocity of 1 km/s at an altitude of 25 km. The kinetic energy is

• A. $1.5\times {10}^{10}$ J
• B. $1.5\times {10}^{12}$ J
• C. $1.2\times {10}^{12}$ J
• D. $1.5\times {10}^8$ J

Answer 1

The correct option is B $1.5\times {10}^{12}$ J

$KE=0.5\times m{v}^2$

$\Rightarrow KE=0.5\times 3\times {10}^6\times (1\times 1000{)}^2=1.5\times {10}^{12}J$

Hence, correct answer is option $B$

Note- Here $PE\ne KE$ because the rocket has accelerated i.e. an external force is applied.