2. A 2,009-kg car is moving down a road with a slope (grade) of 27% while speedi

Question

2. A 2,009-kg car is moving down a road with a slope (grade) of 27% while speeding up at a rate of 1.9 m/s^2. What is the direction and magnitude of the frictional force?

(define positive in the forward direction, i.e., down the slope)?

3. A 1,344-kg car is moving down a road with a slope (grade) of 14% at a constant speed of 18 m/s. What is the direction and magnitude of the frictional force?

(define positive in the forward direction, i.e., down the slope)?

Please explain clearly how you got the answers.. Thank you!!

Explanation / Answer

1.

The friction present is kinetic friction (friction when there is sliding between the two surfaces, in this case the car and

the ground). This friction always points opposite to the direction of motion, in this case up the slope. This means the direction is NEGATIVE.

Now, if this car is slowing down at a rate of 3.4 m/s^2, this is due to a combination of the friction force upwards and the gravitational force downwards. The gravitational force downwards is the sine component of gravity:

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Now, since the car is slowing down, the acceleration is negative. So,

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