You are kidnapped by political-science majors (who are upset because you told them political science is not real science). Although blindfolded, you can tell the speed of their car (by the whine of the engine), the time of travel (by mentally counting off seconds), and the direction of travel (by turns along the rectangular street system). From these clues, you know that you are taken along the following course: 50Km/hfor2.0min, turn 90°to the right,20Km/h for4.0min, turn 90°to the right, 20Km/hfor60s, turn 90°to the left,50Km/hfor60s, turn 90°to the right, 20Km/hfor2.0min, turn90° to the left 50Km/hfor30s. At that point, (a) how far are you from your starting point, and (b) in what direction relative to your initial direction of travel are you?

Short Answer

Expert verified

a) The distance of a kidnapped point from the starting point is 2668m.

b) The direction of travel from the initial point-76°i.e. measured clockwise with respect to the initial direction of motion.

Step by step solution

01

The given data

Speed and the direction of movement along the following course are given as 50km/hfor2min, turn 90°to the right20km/h, for4min, turn60s, turn 90°to the left, 50km/hfor 60s, turn 90°to the right, 20km/hfor2min, turn 90°to the left, 50km/hfor30s.

02

Understanding the concept of the relative motion

The comparison of the relative accelerations and velocities of two rigid entities is referred to as relative motion. Using the formula for the magnitude of the vector, we can find the magnitude of the displacement and direction of the ending point from the starting point.

Formulae:

Magnitude of the resultant vectorVis given by,V=Vx2+Vy2 …(i)

The direction of vector is given by, tanθ=VyVx …(ii)

03

(a) Calculation of the distance of the kidnapped point from the starting point

Distance covered in 2 min at a speed of 50 km/h

vx1=50kmhr×1000m1km×1hr60min×1min60s=13.89m/st1=2min×601min=120s

So, the distance d1is

d1=vx1×t1=13.89m/s×120s=1666.671667m

The distance traveled d2in 4 min at a speed of 20 km/h

vy1=20kmhr×1000m1km×1hr60min×1min60s=5.56m/s

t2=4min×601min=240s

So, the distance d2is

d2=vy1×t2=5.56m/s×240s=1333.331333m

The distance traveled d3in 60 sec at a speed of 20 km/h

vx2=20kmhr×1000m1km×1hr60min×1min60s=5.56m/st3=60s

So, the distance d3is

d3=vx2×t3=5.56m/s×60s=333.33m333m

Distance covered d4in 60 s at a speed of 50 km/h

vy2=50kmhr×1000m1km×1hr60min×1min60s=13.89m/st4=60s

So, the distanced4is

d4=vy2×t4=13.89m/s×60s=833.33m833m

Distance covered d5in 2 min at a speed of 20 km/h

vx3=20kmhr×1000m1km×1hr60min×1min60s=5.56m/st5=2min×60s1min=120s

So, the distance d5is

d5=vx3×t5=5.56m/s×120s=667.2m667m

Distance coveredd6in 30 s at a speed of 50 km/h

vy3=50kmhr×1000m1km×1hr60min×1min60s=13.89m/st6=30s

So, the distance d6is

d6=vy3×t6=13.89m/s×30s=416.66m417m

The distances traveled can be shown in the below diagram. The direction towards right and the upward direction is assumed as positive.

From diagram and calculated values, we can find the net displacement along x-direction as,

X=d1-d3-d5=1667m-333m-667m=667m

From diagram and calculated values, we can find the net displacement along y-direction as,

Y=d2+d4+d6=-1333m+-833m+-417m=-2583m

Therefore, the magnitude of total displacement is given using equation (i) and the above components as follows:

d=667m2+-2583m2=2667.72m2668m

Hence, the magnitude of the distance vector is2668m.

04

(b) Calculation of the direction of the travel from the initial point

The direction of travel from the initial point is given using equation (ii) as follows:

tanθ=-2583m667mθ=tan-1-3.873=-75.52°-76°

Since angle is negative, it means it is measured in clockwise direction with respect to initial direction of motion. Hence, the value of the angle is76°.

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