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A picture frame hung against a wall is suspended by two wires attached to its upper corners. If the two wires make the same angle with the vertical, what must this angle be if the tension in each wire is equal to 0.75 of the weight of the frame? (Ignore any friction between the wall and the picture frame.

Short Answer

Expert verified
The wires must make an angle with the vertical that is approximately \(48.19^\circ\), if the tension in each wire is equal to 0.75 of the weight of the frame.

Step by step solution

01

Identify the Forces Involved

We are dealing with a physics problem about forces and equilibrium. The frame is suspended by two wires and it's at rest (equilibrium state). This means the downward force (weight of the frame) is balanced by the upward forces (the vertical components of the tensions in the wires). Each tension T can be split into two components: \(T\sin(\theta)\) horizontally and \(T\cos(\theta)\) vertically.
02

Apply Equilibrium Conditions

Using the equilibrium conditions, two equations can be written: 1. The sum of vertical forces equals zero, which means the vertical components of tension should sum up to the weight of the frame: \(2T\cos(\theta) = w\)2. The sum of horizontal forces equals zero, which means the horizontal components of the tension should cancel each other out:\(2T\sin(\theta) = 0\)Note that the value of T = 0.75w is given in the problem.
03

Substitute the Given Tension Value and Solve for the Angle

Substitute T value into the equation for vertical equilibrium:\(2(0.75w)\cos(\theta) = w\)Solve the equation above for \(\cos(\theta)\):\(\cos(\theta) = \frac{w}{1.5w} = \frac{2}{3}\)Finally, calculate the angle \(\theta\) using the inverse cosine function:\(\theta = \cos^{-1}(\frac{2}{3})\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Tension in Wires
When you hang a picture frame using wires, the tension in each wire plays a crucial role in keeping it steady. Tension is the force conducted along the wire when it's pulled tight by forces acting from either end. In this exercise, the wires both carry a tension equal to 0.75 times the weight of the frame. Imagine this tension pulling upwards and slightly outwards from each corner of the frame towards the wall where the wires are attached.

It's important to understand that tension can be divided into different force components. These components help explain how the tension stabilizes the hanging object. Whenever you see tension problems, try breaking them down into their vertical and horizontal parts; this step makes complex problems easier to solve.
  • The total tension is divided into vertical and horizontal components.
  • In this scenario, we focus on how this tension balances the downward pull of gravity on the frame.
Breaking down tension in wires will help you see how stability is achieved through equilibrium, where all forces balance out, leaving the frame hanging still.
Angle Calculation
Finding the correct angle each wire makes with the vertical is important when solving this problem. This angle ensures that all forces are balanced, keeping the frame so it won't fall or swing.

From the problem statement, we know the tension is 0.75 times the weight of the frame. Using trigonometry and equilibrium equations, we can calculate the angle accurately. With a basic understanding of triangles and angles, you can calculate this angle using the cosine function. The equation we used comes from acknowledging that for the vertical forces to balance and achieve equilibrium:
  • First, we have \(2T\cos(\theta) = w\), where \(w\) is the weight and \(T = 0.75w\).
  • Simplifying gives \(\cos(\theta) = \frac{2}{3}\).
  • To find \(\theta\), you take the inverse cosine of \(\frac{2}{3}\).
With this approach, the angle calculation shows how a bit of geometry can solve practical problems.
Vertical Force Components
Understanding vertical force components is important in this scenario because they are responsible for balancing out the weight of the frame. The vertical components of the tension in the wires counteract the gravitational pull.

Here is how the components work:
  • Each wire contributes a vertical force upwards, represented as \(T\cos(\theta)\).
  • Since two wires support the frame, we double this contribution: \(2T\cos(\theta)\).
  • This upward force equals the weight of the frame, \(w\), when equilibrium is achieved.
This part of the problem reminds you that for any object in equilibrium, the upward forces must exactly counterbalance the downwards forces exerted by gravity.
Horizontal Force Components
In equilibrium problems like this one involving wires, it's vital to examine the horizontal force components, even if they seem less obvious than the vertical components.

Horizontal components can be thought of as the forces that pull inwards toward the center of the frame, from each wire:
  • Each wire has a horizontal component, \(T\sin(\theta)\), acting away from the frame.
  • Since they are equal in magnitude and opposite in direction, they cancel each other out.
  • This cancellation ensures the frame doesn't move sideways, maintaining stability.
Balancing these horizontal forces is as crucial as managing vertical forces for achieving overall equilibrium. They reinforce the significance of dissecting forces into components to understand their complete effect.

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Most popular questions from this chapter

A box with mass \(m\) sits at the bottom of a long ramp that is sloped upward at an angle \(\alpha\) above the horizontal. You give the box a quick shove, and after it leaves your hands it is moving up the ramp with an initial speed \(v_{0}\). The box travels a distance \(d\) up the ramp and then slides back down. When it returns to its starting point, the speed of the box is half the speed it started with; it has speed \(v_{0} / 2 .\) What is the coefficient of kinetic friction between the box and the ramp? (Your answer should depend on only \(\alpha\).)

A large crate with mass \(m\) rests on a horizontal floor. The coefficients of friction between the crate and the floor are \(\mu_{\mathrm{s}}\) and \(\mu_{\mathrm{k}} .\) A woman pushes downward with a force \(\overrightarrow{\boldsymbol{F}}\) on the crate at an angle \(\theta\) below the horizontal. (a) What magnitude of force \(\vec{F}\) is required to keep the crate moving at constant velocity? (b) If \(\mu_{\mathrm{s}}\) is greater than some critical value, the woman cannot start the crate moving no matter how hard she pushes. Calculate this critical value of \(\mu_{\mathrm{s}}\)

A box of mass \(12.0 \mathrm{~kg}\) sits at rest on a horizontal surface. The coefficient of kinetic friction between the surface and the box is \(0.300 .\) The box is initially at rest, and then a constant force of magnitude \(F\) and direction \(37.0^{\circ}\) below the horizontal is applied to the box; the box slides along the surface. (a) What is \(F\) if the box has a speed of \(6.00 \mathrm{~m} / \mathrm{s}\) after traveling a distance of \(8.00 \mathrm{~m} ?\) (b) What is \(F\) if the surface is friction less and all the other quantities are the same? (c) What is \(F\) if all the quantities are the same as in part (a) but the force applied to the box is horizontal?

A flat (unbanked) curve on a highway has a radius of \(170.0 \mathrm{~m}\). A car rounds the curve at a speed of \(25.0 \mathrm{~m} / \mathrm{s}\). (a) What is the minimum coefficient of static friction that will prevent sliding? (b) Suppose that the highway is icy and the coefficient of static friction between the tires and pavement is only one-third of what you found in part (a). What should be the maximum speed of the car so that it can round the curve safely?

A racetrack curve has radius \(90.0 \mathrm{~m}\) and is banked at an angle of \(18.0^{\circ} .\) The coefficient of static friction between the tires and the roadway is \(0.400 .\) A race car with mass \(1200 \mathrm{~kg}\) rounds the curve with the maximum speed to avoid skidding. (a) As the car rounds the curve, what is the normal force exerted on it by the road? What are the car's (b) radial acceleration and (c) speed?

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