What is the minimum work needed to push a 800 kg car 900m up along a 8.0 incline

Question

What is the minimum work needed to push a 800 kg car 900m up along a 8.0 incline?

Part A

Ignore friction.

Express your answer using two significant figures.

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Part B

Assume the effective coefficient of friction retarding the car is 0.25.

Express your answer using two significant figures.

What is the minimum work needed to push a 800 kg car 900m up along a 8.0 incline?

Part A

Ignore friction.

Express your answer using two significant figures.

SubmitMy AnswersGive Up

Part B

Assume the effective coefficient of friction retarding the car is 0.25.

Express your answer using two significant figures.

Explanation / Answer

a) If there is no friction, the work done is just the potential energy delivered.

height = 900*sin 8° = 125 m

Work done in lifting car to this height = m*g*h
Work = 800*9.81*125
Work = 983007.4J

b)

Now you have to account for the friction:

Coefficient of friction = 0.25.
Frictional force retarding motion = 0.25m*g*cos 8°
friction force = 0.25*800*9.81*0.990
Frictional force = 1942.9N
Work done against friction = Force * distance
Work done against friction = 1942.38*900 = 1748142J

Total work done = 983007+ 1748142= 2731149J

Work required = 2.7*10^6J

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