Calculating Avg Velocity of Car in Rural Rally

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The discussion focuses on calculating the average velocity of a car in a rural rally, where the speed limit is 80 km/h. The total displacement is determined to be 31 km east, while the total distance traveled is 107 km. The user calculates the time taken at maximum speed, resulting in an average velocity of 23.1 km/h east. However, the textbook provides an answer of 25 km/h east, prompting a question about the discrepancy. The conversation highlights the importance of considering speed limits and the assumptions made in the calculations.
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Homework Statement



The motion depicted in Figure 1 shows the path of a team in a car rally held in a rural area where the speed limit is 80 km/h. In the car rally, points are deducted for anyone determined to be breaking the speed limit.

c) Determine the average velocity (magnitude and direction) of the car's motion for the entire trip.

The race track kind of looks like the one I attached.


side A = 23 km = side C
side B = 46 km
that small part, D = 15 km
x = start
v, >, <, ^ show the direction.

Homework Equations



Vavg = (delta x)/(delta t)

The Attempt at a Solution



(I already did the first parts)
The total displacement (delta x) is from x to D. So that would be 46-15 = 31 km.
Total time is ?? Assuming that they don't surpass the speed limit, they are going 80km/h. Knowing that, and that they go a total of 107 km... (46+23+23+15) ... they will take 1. 3375h. So...then wouldn't it be 31/1.3375 = 23.1 km/h [E] (East because displacement is only eastward)

The answer the book gave was 25 km/h [E].
What'd I do wrong??
 

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Your answer looks OK to me. (Even though you assume that the car always travels at its maximum speed. :wink:)
 
Silly textbook...

Thanks!
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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