📚 Learning Guide
Friction Forces Analysis
medium

If a block weighing 20 kg is placed on a 45-degree incline, and the coefficient of static friction between the block and the incline is 0.6, what is the maximum angle at which the block can remain at rest without sliding down?

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Choose the Best Answer

A

Approximately 31 degrees

B

Approximately 45 degrees

C

Approximately 60 degrees

D

Approximately 75 degrees

Understanding the Answer

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Answer

The block stays put when the static‑friction force can counter the downhill pull of gravity. The downhill pull is \(mg\sin\theta\) and the friction force is at most \(\mu_s N = \mu_s mg\cos\theta\). Setting the two equal gives \(\mu_s mg\cos\theta = mg\sin\theta\), so \(\tan\theta = \mu_s\). With \(\mu_s = 0. 6\), the largest angle is \(\theta = \arctan(0.

Detailed Explanation

Static friction stops the block when the downhill pull is just equal to the friction force that can act. Other options are incorrect because Some think the block can stay on the 45° incline itself because the slope is 45°; A few students guess 60° because they confuse the coefficient with a direct angle.

Key Concepts

Angle of Incline Impact
Static Friction Coefficient
Topic

Friction Forces Analysis

Difficulty

medium level question

Cognitive Level

understand

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