Explanation

To calculate the velocity attained by the rocket, we can use the equation:

F × t = m × Δv

where:

F = force applied (5 × 10^5 N)

t = time (20 s)

m = mass of the rocket (2 × 10^4 kg)

Δv = change in velocity (final velocity - initial velocity)

Since the rocket starts from rest, the initial velocity is 0. Therefore, Δv = final velocity.

Rearranging the equation to solve for Δv, we get:

Δv = F × t / m

= (5 × 10^5 N) × (20 s) / (2 × 10^4 kg)

= 500 m/s