Question

question 15
1 pts
an object is moving down an adjustable ramp at some velocity initially. as the angle of the ramp is increased, what happens to the magnitude of the kinetic friction force that acts on the object, and why?
the friction force increases, because the normal force decreases as the angle increases
the friction force decreases, because the normal force decreases as the angle increases
the friction force decreases, because the normal force increases as the angle increases
the friction force increases, because the normal force increases as the angle increases
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Explanation:

The formula for kinetic friction force is \(F_{k}=\mu_{k}N\), where \(\mu_{k}\) is the coefficient of kinetic friction (constant for given surfaces) and \(N\) is the normal force. For an object on a ramp of angle \(\theta\), the normal force \(N = mg\cos\theta\). As \(\theta\) increases, \(\cos\theta\) decreases (since \(\cos\theta\) is a decreasing function in the range \(0\leq\theta\leq90^{\circ}\)). Since \(F_{k}\propto N\) (because \(\mu_{k}\) is constant), when \(N\) decreases, \(F_{k}\) also decreases.

Answer:

The friction force decreases, because the normal force decreases as the angle increases.