1. **State the problem:** A train with mass 100t (100,000 kg) accelerates from rest to 720 kph in 50 seconds. We need to find: - Average acceleration - Force required to produce this acceleration - Inertia force on the train 2. **Convert units:** - Velocity from 720 kph to m/s: $$720 \text{ kph} = 720 \times \frac{1000}{3600} = 200 \text{ m/s}$$ 3. **Calculate average acceleration:** Using the formula for acceleration: $$a = \frac{\Delta v}{\Delta t}$$ where $\Delta v = 200 - 0 = 200$ m/s and $\Delta t = 50$ s. $$a = \frac{200}{50} = 4 \text{ m/s}^2$$ 4. **Calculate force required:** Using Newton's second law: $$F = m \times a$$ where $m = 100,000$ kg and $a = 4$ m/s$^2$. $$F = 100,000 \times 4 = 400,000 \text{ N}$$ 5. **Inertia force:** The inertia force is the force needed to overcome the train's resistance to acceleration, which is the same as the force calculated above: $$F_{inertia} = 400,000 \text{ N}$$ **Final answers:** - Average acceleration: $4$ m/s$^2$ - Force required: $400,000$ N - Inertia force: $400,000$ N