1. **Problem statement:** Two forces of magnitudes 3N and 4N act perpendicular to each other on a 2kg object initially at rest. Find the kinetic energy after 20 seconds. 2. **Step 1: Find the resultant force.** Since the forces are perpendicular, use the Pythagorean theorem: $$F_{res} = \sqrt{3^2 + 4^2} = \sqrt{9 + 16} = \sqrt{25} = 5\,N$$ 3. **Step 2: Calculate acceleration using Newton's second law:** $$a = \frac{F_{res}}{m} = \frac{5}{2} = 2.5\,m/s^2$$ 4. **Step 3: Calculate the velocity after 20 seconds:** Since initial velocity $u=0$ (at rest), $$v = u + at = 0 + 2.5 \times 20 = 50\,m/s$$ 5. **Step 4: Calculate kinetic energy using the formula:** $$KE = \frac{1}{2} m v^2$$ 6. **Step 5: Substitute values:** $$KE = \frac{1}{2} \times 2 \times 50^2 = 1 \times 2500 = 2500\,J$$ **Final answer:** The kinetic energy of the object after 20 seconds is $2500$ joules.