Forces and kinetic energy problem

AI Thread Summary
Shawn rides his bike with a total mass of 43.5 kg at a constant velocity of approximately 2.08 m/s over a distance of 1.3 km in 10.4 minutes. To find his kinetic energy, the formula used is KE = 1/2 * m * v^2. After calculations, the correct kinetic energy is determined to be approximately 45.31 J, not the initially mentioned 94.40 J. The discussion highlights the importance of understanding the kinetic energy formula and proper unit conversions. Overall, the problem emphasizes the application of basic physics principles to solve for kinetic energy.
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Homework Statement


Shawn and his bike have a total mass of 43.5 kg. Shawn rides his bike 1.3 km in 10.4 min at a constant velocity.
The acceleration of gravity is 9.8 m/s^2
What is Shawn's kinetic energy?


Homework Equations


F = ma
Ff = u * Fn
Fn = mg
avgV = x/t
x = 1/2(Vf + Vi)t


The Attempt at a Solution



ok so I converted km to m and min to s:
x = 1300m
t = 624s
and then i used avgV = x/t so avgV = ~2.08333 m/s

i have no idea what kinetic energy is, this hasn't been covered in class yet but I wanted to get ahead because I think I am coming down with the flu. The answer to the problem is supposed to be 94.4014 J but I have no idea how to set this problem up to get this. Please help me! Thanks.
 
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The kinetic energy = 1/2*m*v^2
 
THAAATTSS what i needed ooohhh maaann thanks rl.bhat!
so it would be (0.5)(43.5)(2.08333)^2 = 45.3124 J

thanks again!
 
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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