NSEP Prep-2019

When you start your stopwatch, a particle moving on the x -axis is observed somewhere between the positions x = 10 m and x = 12 m. Sometime during the fourth second, it passes the position x = 22 m and at the instant t = 12 s it is observed somewhere between the positions x =55 m and x = 60 m. If the particle is moving with uniform velocity, when do you expect its arrival at the position x = 88 m??

None of these between 19.5 s and 21 s between 21.5 s and 23.5 s between 21 s and 24 s between 19.5 s and 20.5 s

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2 solutions

Steven Chase
May 17, 2019

This is easy enough to do by searching the parameter space ( 10 x 1 12 ) (10 \leq x_1 \leq 12) and ( 55 x 2 60 ) (55 \leq x_2 \leq 60) , and by applying the "fourth second" qualifying condition.

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import math

N = 2000

#####################################

tfmax = 0.0
tfmin = 9999999999.0

dx1 = (12.0 - 10.0)/N   # Increments for x1,x2
dx2 = (60.0 - 55.0)/N

#####################################

x1 = 10.0

while x1 <= 12.0:   # search x1 between 10 and 12

    x2 = 55.0

    while x2 <= 60.0: # search x2 between 55 and 60

        v = (x2 - x1)/12.0  # speed from t = 12 condition

        #22.0 = x1 + v*tm 

        tm = (22.0 - x1)/v  # calculate time to pass x = 22

        if (tm >= 3.0) and (tm <= 4.0): # tm must be between 3 and 4
            qual = 1                    # this is the qualifying condition
        else:
            qual = 0

        tf = (88.0 - x1)/v      # calculate time to reach 88 meters

        if (tf > tfmax) and (qual == 1):  # store tfmin/tfmax, supervised by qual
            tfmax = tf

        if (tf < tfmin) and (qual == 1):
            tfmin = tf

        x2 = x2 + dx2

    x1 = x1 + dx1

#####################################

# Results

print tfmin  # 19.5
print tfmax  # 21.0

Man you are a legend. I never thought using this

Debarghya Adhikari - 2 years ago

Thanks. How did you do it?

Steven Chase - 2 years ago

Kinematics and with a bit of calculus. No need of algorithms

Debarghya Adhikari - 2 years ago

Hint: Try to find the least and greatest speeds satisfying the consitions

@Debarghya Adhikari in which class you are

A Former Brilliant Member - 1 year, 11 months ago

I am in class 9.In which class you are???

Debarghya Adhikari - 1 year, 10 months ago

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