The conservation of energy always holds true even when not clearly observable in machines that are less than 100% efficient. More often than not a machine will suffer energy losses (e.g. consider for a cooling fan: friction between the rotating blades, drag resistance in the air the fan is pushing around, resistance in the wire, and heat radiating/conducting away from the circuitry).
Answer:
0.34
Explanation:
2.5 Mg = 2500 kg
The change in speed from 100 km/h to 40 km/h is

The deceleration caused by friction force is the change in speed per unit of time

Using Newton 2nd law we can calculate the friction force that caused this deceleration:
F = ma = 2500 * 3.33 = 8333 N
Let g = 9.8m/s2. Friction force is the product of normal (gravity) force and friction coefficient


That will depend on the coefficient of friction between the sliding surfaces, and also on Zak's weight. We don't have any of that information.