Dear swetlina,

When a rocket is fired then as it moves verticaly upwards its kinetic potential energy increases at the expense of its kinetic energy. and it acquires maximum height at a point where its potentil energy is equal to its initial kinetic energy.

However, due atmospheric resistance offered, only 80 percent of its kinetic energy is getting converted into potential energy

so use the formula

(80/100)(1/2m*2000*2000)= maximum potential energy