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The total mass is 2300kg (weight = 5072lbs). Find the size of the force due to wind and rolling friction when the van speed is 44.86mph (1mph= 0.447m/s).


I am really at a loss of what to do here.

Part 2:

How much net power, in hp (1 hp=746W) must the engine deliver to maintain a speed of 44.86mph (20.05m/s) (Neglect losses involved in delivering the power).

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closed as off-topic by Brandon Enright, John Rennie, Kyle Kanos, Chris White, jinawee Mar 13 '14 at 15:51

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Are you meant to calculate the acceleration from the graph? – Jed Mar 12 '14 at 5:07
no... Bad tag, I fixed it. – user2840324 Mar 12 '14 at 5:09
up vote 0 down vote accepted

Based on the graphed data, the acceleration appears constant and I estimate it at $$ a = \frac{40-55}{25-5} = -0.75 \text{ mph/s} = -0.33528 \text{ m / (s$^2$)}$$ You know the mass is 2300 kg, so you can just plug in to get the force of friction using $$ F = ma $$

As for the power, I believe (please check this) that in your 1D case, the power is given as $P = Fv$ where $v$ is the velocity.

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Thank you very much. – user2840324 Mar 12 '14 at 6:21
Please don't post complete answers to homework-like questions in the future, as mentioned in our homework policy. – David Z Mar 14 '14 at 18:19

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