Final answer:
The acceleration produced by the brakes is -2 m/s² and the distance covered by the train before coming to rest is 100 meters. The correct answer is option C.
Step-by-step explanation:
In order to determine the acceleration produced by the brakes, we need to convert the speed from kilometers per hour to meters per second.
The conversion factor is 1000 meters = 1 kilometer and 1 hour = 3600 seconds.
So, the speed of the train in meters per second is
72 km/hr * (1000 m/1 km) * (1 hr/3600 s) = 20 m/s.
Next, we can use the formula for acceleration, which is acceleration (a) = change in velocity (Δv) / change in time (Δt).
In this case, the change in velocity is 20 m/s - 0 m/s = 20 m/s, and the change in time is 10 seconds.
So, the acceleration is 20 m/s / 10 s = 2 m/s².
To find the distance covered by the train before coming to rest, we can use the formula for distance, which is
distance (s) = initial velocity (u) * time (t) + 0.5 * acceleration (a) * time^2.
In this case, the initial velocity is 20 m/s, the time is 10 seconds, and the acceleration is -2 m/s² (negative because the train is slowing down).
Plugging in these values, we get:
distance (s) = 20 m/s * 10 s + 0.5 * (-2 m/s²) * (10 s)^2
= 200 m - 100 m = 100 m.
Therefore, the correct answer is option D. a=−2 m/s², s=100m.