Two wave pulses pass each other on a string. The pulse traveling toward the right has positive amplitude, whereas the pulse trav
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Answer:
a) t = 746 s
b) t = 666 s
Explanation:
a)
- Total time will be the sum of the partial times between stations plus the time stopped at the stations.
- Due to the distance between stations is the same, and the time between stations must be the same (Because the train starts from rest in each station) we can find total time, finding the time for any of the distance between two stations, and then multiply it times the number of distances.
- At any station, the train starts from rest, and then accelerates at 1.1m/s2 till it reaches to a speed of 95 km/h.
- In order to simplify things, let's first to convert this speed from km/h to m/s, as follows:
- Applying the definition of acceleration, we can find the time traveled by the train before reaching to this speed, as follows:
- Next, we can find the distance traveled during this time, assuming that the acceleration is constant, using the following kinematic equation:
- In the same way, we can find the time needed to reach to a complete stop at the next station, applying the definition of acceleration, as follows:
- We can find the distance traveled while the train was decelerating as follows:
- Finally, we need to know the time traveled at constant speed.
- So, we need to find first the distance traveled at the constant speed of 26.4m/s.
- This distance is just the total distance between stations (3.0 km) minus the distance used for acceleration (x₁) and the distance for deceleration (x₃), as follows:
- x₂ = L - (x₁+x₃) = 3000 m - (316.8 m + 158.4 m) = 2525 m (6)
- The time traveled at constant speed (t₂), can be found from the definition of average velocity, as follows:
- Total time between two stations is simply the sum of the three times we have just found:
- t = t₁ +t₂+t₃ = 24 s + 95.6 s + 12 s = 131.6 s (8)
- Due to we have six stations (including those at the ends) the total time traveled while the train was moving, is just t times 5, as follows:
- tm = t*5 = 131.6 * 5 = 658.2 s (9)
- Since we know that the train was stopped at each intermediate station for 22s, and we have 4 intermediate stops, we need to add to total time 22s * 4 = 88 s, as follows:
- Ttotal = tm + 88 s = 658.2 s + 88 s = 746 s (10)
b)
- Using all the same premises that for a) we know that the only difference, in order to find the time between stations, will be due to the time traveled at constant speed, because the distance traveled at a constant speed will be different.
- Since t₁ and t₃ will be the same, x₁ and x₃, will be the same too.
- We can find the distance traveled at constant speed, rewriting (6) as follows:
- x₂ = L - (x₁+x₃) = 5000 m - (316.8 m + 158.4 m) = 4525 m (11)
- The time traveled at constant speed (t₂), can be found from the definition of average velocity, as follows:
- Total time between two stations is simply the sum of the three times we have just found:
- t = t₁ +t₂+t₃ = 24 s + 171.4 s + 12 s = 207.4 s (13)
- Due to we have four stations (including those at the ends) the total time traveled while the train was moving, is just t times 3, as follows:
- tm = t*3 = 207.4 * 3 = 622.2 s (14)
- Since we know that the train was stopped at each intermediate station for 22s, and we have 2 intermediate stops, we need to add to total time 22s * 2 = 44 s, as follows:
- Ttotal = tm + 44 s = 622.2 s + 44 s = 666 s (15)
The related concept to solve this exercise is given in the expressions that the magnetic field has both as a function of the number of loops, current and length, as well as inductance and permeability. The first expression could be given as,
The magnetic field H is given as,
Here,
n = Number of turns of the coil
I = Current that flows in the coil
l = Length of the coil
From the above equation, the number of turns of the coil is,
The magnetic field is again given by,
Where the minimum inductance produced by the solenoid coil is B.
We have to obtain n, that
Replacing with our values we have that,
Therefore the number of turn required is 28Truns