A 200 kg, 10 m-long beam is held at equilibrium by a hinge on the floor and a force you apply on it via a light rope connected to its edge, as shown. The beam is held at 53° above the horizontal, and your rope makes an angle of 30° with it. Calculate the angle that the Net Force of the hinge makes with the horizontal (use +/– for above/below +x, and use g=10 m/s2.)
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More 2D Equilibrium Problems
Problem 63b
Textbook Question
FIGURE P12.63 shows a 15 kg cylinder held at rest on a 20° slope. What is the magnitude of the static friction force?


1
Identify the forces acting on the cylinder: The forces include the gravitational force (weight), the normal force exerted by the slope, and the static friction force. The weight of the cylinder is given by \( F_g = m \cdot g \), where \( m = 15 \; \text{kg} \) and \( g = 9.8 \; \text{m/s}^2 \).
Resolve the gravitational force into components parallel and perpendicular to the slope. The parallel component is \( F_{g, \parallel} = F_g \cdot \sin(\theta) \), and the perpendicular component is \( F_{g, \perp} = F_g \cdot \cos(\theta) \), where \( \theta = 20^\circ \).
Recognize that the cylinder is at rest, meaning the static friction force must exactly balance the parallel component of the gravitational force. Therefore, \( f_s = F_{g, \parallel} \).
Substitute the expressions for \( F_g \) and \( F_{g, \parallel} \) into the equation for static friction: \( f_s = m \cdot g \cdot \sin(\theta) \).
Plug in the known values for \( m \), \( g \), and \( \theta \) to calculate the magnitude of the static friction force. Ensure that the units are consistent throughout the calculation.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Static Friction
Static friction is the force that prevents an object from starting to move when a force is applied. It acts parallel to the surface of contact and varies in magnitude up to a maximum value, which is determined by the coefficient of static friction and the normal force. In this scenario, it is crucial to calculate the static friction force to determine if the cylinder will remain at rest on the slope.
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Static Friction & Equilibrium
Normal Force
The normal force is the perpendicular force exerted by a surface to support the weight of an object resting on it. On an inclined plane, the normal force is less than the object's weight and can be calculated using the angle of the slope. Understanding the normal force is essential for determining the static friction force acting on the cylinder.
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The Normal Force
Forces on an Incline
When an object is on an inclined plane, the forces acting on it include gravitational force, normal force, and frictional force. The gravitational force can be resolved into components parallel and perpendicular to the slope. Analyzing these forces helps in calculating the static friction force required to keep the object at rest against the pull of gravity down the slope.
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Intro to Inclined Planes
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