# Understanding Physics Problems

## How many seconds does it take for a normal tractor-trailer to clear a double track?

**Final answer:** The provided information pertains to various physics problems rather than the specific question of a tractor-trailer clearing a double track. One example includes a truck with specific velocity and deceleration parameters in relation to stopping distance, indicating it will not hit a child 50 meters away.

## Explanation:

The question asks for the time it takes for a normal tractor-trailer to clear a double track, but given the provided information, it seems there's a confusion as the details do not pertain to a tractor-trailer but instead a car's braking situation and various physics problems. Therefore, to compute the time it takes for an actual tractor-trailer to clear a double track, we would need additional specifics such as the length of the double track, and the speed at which the tractor-trailer is traveling.

However, if we were to tackle the truck scenario mentioned: A truck traveling at a constant velocity of 10 m/s with a reaction time of 0.5 seconds, begins to decelerate at -1.25 m/s² upon seeing a child 50 meters away. To determine if the truck will hit the child, we calculate the stopping distance of the truck using the formula d = v²/(2a), where d is the stopping distance, v is the velocity, and a is the deceleration. We also account for the distance covered during the driver's reaction time.

The distance covered during the driver's reaction time is velocity multiplied by reaction time (v*t), which equals 10 m/s * 0.5 s = 5 m. The stopping distance using the formula is (10 m/s)² / (2*(-1.25 m/s²)) = 40 m. Adding the reaction distance to the braking distance, the truck travels a total of 5 m + 40 m = 45 m to stop, which means the truck will not hit the child, as the total stopping distance is less than 50 m.