Given data

• Mass of body: $m = 2\,\text{kg}$
• Starts from rest: $u = 0$
• Kinetic energy at the end of $5^{\text{th}}$ second: $K = 10000\,\text{J}$

Use kinetic energy formula $K = \frac{1}{2}mv^2$ Substituting the values: $10000 = \frac{1}{2}(2)v^2$ $10000 = v^2$ $v = 100\,\text{m/s}$

Find acceleration Since the body starts from rest and reaches $v=100\,\text{m/s}$ in $t=5\,\text{s}$, $v = u + at$ $100 = 0 + a(5)$ $a = 20\,\text{m/s}^2$

Find force Using Newton's second law, $F = ma$ $F = 2 \times 20 = 40\,\text{N}$

Final answer The force acting on the body is: $\boxed{40\,\text{N}}$