Consider a railroad bridge over a highway. A train passing over the bridge dislodges a loose bolt from the bridge, which proceed
s to fall straight down and ends up breaking the windshield of a car passing under the bridge. The car was 27 m away from the point of impact when the bolt began to fall down; unfortunately, the driver did not notice it and proceeded at constant speed of 17 m/s. How high is the bridge? Or more precisely, how high are the railroad tracks above the windshield height? The acceleration due to gravity is 9.8 m/s 2 . Answer in units of m
Hello! To solve this problem we must consider the following:
1. The car moves with constant speed, which means that the distance traveled is equal to the multiplication of time by speed.
X = VT
we solve the equation for time
2. The bolt moves with constant acceleration, with acceleration of 9.81m / s ^ 2, so we could apply the following equation.
note=remember that "a uniformly accelerated motion", means that if the velocity is plotted with respect to time we will find a line and its slope will be the value of the acceleration, it determines how much it changes the speed with respect to time.
Since no friction present, assuming no external forces acting during the three collisions, total momentum must be conserved.
For the first collission, only mass 1 is moving before it, so we can write the following equation:
Since both masses are identical, and they stick together after the collision, we can express the final momentum as follows:
From (1) and (2) we get:
v₁ = v₀/2 (3)
Since the masses are moving on a frictionless 1D track, the speed of the set of mass 1 and 2 combined together before colliding with mass 3 is just v₁, so the initial momentum prior the second collision (p₁) can be expressed as follows:
Since after the collision the three masses stick together, we can express this final momentum (p₂) as follows:
From (4) and (5) we get:
v₂ = v₀/3 (6)
Since the masses are moving on a frictionless 1D track, the speed of the set of mass 1, 2 and 3 combined together before colliding with mass 4 is just v₂, so the initial momentum prior the third collision (p₂) can be expressed as follows:
Since after the collision the four masses stick together, we can express this final momentum (p₃) as follows:
From (7) and (8) we get:
v₃ = v₀/4
This means that after the last collision, the speed will have been reduced to a 25% of the initial value, so it will have been reduced in a 75% regarding the initial value of v₀.