Power of Brakes in 1452 kg Car: 4501.2 W

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The discussion revolves around calculating the power developed by the brakes of a 1452 kg car that stops from a speed of 17.2 m/s over a distance of 100 m in 6.2 seconds. The initial calculations for work done (W) were determined to be 214,779.84 J, leading to a power output (P) of 4501.2 W. However, participants pointed out errors in the calculations, suggesting that the correct power output should be around 34,700 watts. The importance of using accurate values and proper mathematical operations was emphasized to arrive at the correct answer. Accurate calculations are crucial for solving physics problems effectively.
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Homework Statement


The brakes of a 1452 kg car bring it to a stop from a speed of 17.2 m/s in a distance of 100 m. If the car originally stops in 6.2 s (100 m), what power is developed by the brakes?


Homework Equations


W = FF Δs
W = ½ m· v^2
P = W/t
P = F * v


The Attempt at a Solution


W = 1/2 * m * v^2
W = 1/2 * 1452 kg * 6.2 s ^2
W = 214779.84 J

P = W/t
P = 214779.84 J/6.2 s
P = 4501.2 W

I know that this isn't correct because it is a multiple choice study guide. The options are the following:

a. 230 kW
b. 34.7 kW
c. 23.4 kW
d. 2.15 kW

It is the only problem I can't solve, and I'd like to know how to! Thank you.
 
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HazelDryad said:

Homework Statement


The brakes of a 1452 kg car bring it to a stop from a speed of 17.2 m/s in a distance of 100 m. If the car originally stops in 6.2 s (100 m), what power is developed by the brakes?


Homework Equations


W = FF Δs
W = ½ m· v^2
P = W/t
P = F * v


The Attempt at a Solution


W = 1/2 * m * v^2
W = 1/2 * 1452 kg * 6.2 s ^2
v= 17.2
W = 214779.84 J
yes..
P = W/t
P = 214779.84 J/6.2 s
P = 4501.2 W
but 214780/6.2 = 34,700 watts. Just check your math. You were putting in wrong numbers or dividing incorrectly, or both...
 
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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