To calculate the work required to increase the speed of a 4 kg object from 20 m/s to 40 m/s, we need to use the formula:
work = 0.5 × mass × (final velocity^2 - initial velocity^2)
Here, the mass of the object is 4 kg, the initial velocity is 20 m/s, and the final velocity is 40 m/s.
So, work = 0.5 × 4 × (40^2 - 20^2)
= 0.5 × 4 × (1600 - 400)
= 0.5 × 4 × 1200
= 2400 joules
Therefore, the work required to increase the speed of a 4 kg object from 20 m/s to 40 m/s is 2400 joules.