Finding initial velocity given displacement, time, and final velocity

AI Thread Summary
The discussion centers on calculating the initial velocity of a woman who accelerates uniformly while running 253 meters in 6.12 seconds, reaching a final velocity of 5.05 m/s. The initial attempt at solving the problem resulted in an average velocity calculation of 41.34 m/s, which seems implausible given the final velocity stated. Participants express confusion over the discrepancy between the calculated average velocity and the final velocity. The equations provided, vf = vi + at and v = (xf - xi)/t, are relevant for solving the problem but lead to contradictory results. Overall, the discussion highlights the need for clarity in the problem's parameters and the calculations involved.
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Homework Statement


A woman running at constant velocity speeds up and accelerates uniformly to the west by running 253 m west in 6.12 s. ff she ends up getting up to a velocity of 5.05 m/s w, how fast was she going originally? If she had run the same disance in 5.50 s, what would her average velocity have been during her acceleration?
vf = final velocity = 5.5m/s
x = displacement = 253m
t = 6.12 s
find vi?

Homework Equations


vf=vi+at
v=(xf-xi)/t

The Attempt at a Solution


I honestly am stumped on this question.
average velocity during the acceleration 253/6.12 =41.34 m/s
 
Physics news on Phys.org
This woman would be running at like 100 miles per hour, and then the problem says she ends up "getting up to" a velocity of 5.05 m/s. Something's wrong here.
 
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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