Waiting for a Friend: Solving a Time Difference Problem

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To solve the problem of waiting time between two friends driving different speeds over the same distance, the speeds of 91.4 km/hr and 88.3 km/hr were used to calculate travel times of approximately 0.547 hours and 0.566 hours, respectively. The initial calculation of the waiting time as 0.019 hours was deemed incorrect by the exercise system. Participants suggested that the discrepancy might be due to expectations regarding significant figures or required time units. Clarification on the expected format for the answer could resolve the issue. Accurate interpretation of the problem's requirements is crucial for obtaining the correct solution.
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Homework Statement



You and a friend each drive 50 km. You travel at a uniform speed of 91.4 km/hr and your friend travels at a constant speed of 88.3 km/hr. How long will you wait for your friend?


Homework Equations





The Attempt at a Solution



So I thought I could just set up a ratio and cross-multiply to get the hrs. traveled by each person. I got .547hrs. for "me" and .566hrs. for "my friend". Then subtract, the difference being the answer. However, I am doing this on a computer-generated exercise and it is telling me that .019hrs. is incorrect. Why isn't this right?
 
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It looks like you did this correctly, I get the same answer. It could be they expect a different number of significant figures in the answer, or they expect different time units for some reason.
 
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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