Kinetic energy:

Energy that a body has when it is in motion.

Kinetic energy KE = \frac{1}{2} mv^2   where, m - mass of the body and v - body velocity.

The kinetic energy formula is used to measure the body's mass, velocity, or kinetic energy if any of the other two numerics is given.

Step 1: Using the kinetic energy formula, calculate the object's speed.

Given that

Mass of the truck m = 5000 kg

Kinetic energy of the truck = 400000 joules

KE = \frac{1}{2}mv^2

v^2 = \frac{2 * KE}{m}

\therefore Velocity v = \sqrt{\frac{2 * KE}{m}}

Inserting the known values into the above equation

v = \sqrt{\frac{2 * 400000 J}{5000 kg}}   

v = \sqrt{\frac{800}{5}} = \sqrt{160}

v = 12.64

Thus, speed of the truck v = 12.64 m/s