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Two forces have the same magnitude \(F .\) What is the angle between the two vectors if their sum has a magnitude of (a) 2\(F ?\) (b) \(\sqrt{2} F ?(\mathrm{c})\) zero? Sketch the three vectors in each case.

Short Answer

Expert verified
(a) 0° (b) 90° (c) 180°.

Step by step solution

01

Understanding Forces and Their Sum

We have two forces of the same magnitude, denoted as \( F \). We need to determine the angle between these forces for three different scenarios concerning the magnitude of their sum. The vector sum of two forces is affected by the angle between them.
02

Case (a): Sum Magnitude is 2F

If the sum of the forces has a magnitude of \( 2F \), this means the two vectors are in the same direction. Therefore, the angle between them is \( 0^\circ \). Mathematically, the sum can be represented as \( F + F = 2F \), confirming the forces align completely.
03

Case (b): Sum Magnitude is \(\sqrt{2}F\)

For the sum of the forces to have a magnitude of \( \sqrt{2}F \), we use the formula for the magnitude of the sum of two vectors: \( |\mathbf{A} + \mathbf{B}| = 2F \cos(\theta/2) \). Setting \( 2F \cos(\theta/2) = \sqrt{2}F \), we solve for \( \theta \). This implies \( \cos(\theta/2) = \frac{1}{\sqrt{2}} \), leading to \( \theta/2 = 45^\circ \), so \( \theta = 90^\circ \). The two forces are perpendicular to each other.
04

Case (c): Sum Magnitude is Zero

If the magnitude of the sum of the forces is zero, it implies the vectors are directly opposite to each other. Thus, the angle between them is \( 180^\circ \). Mathematically, \( F - F = 0 \) ensures the forces are exactly opposite.
05

Sketching the Vectors

For case (a), draw both vectors in the same direction. In case (b), draw the vectors at a right angle (90 degrees) to each other. For case (c), the vectors should be in opposite directions, forming a straight line (180 degrees). These visualizations help understand the scenarios for each result.

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Key Concepts

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

Vectors
Vectors are incredibly useful in physics as they allow us to describe quantities that have both magnitude and direction. Think of them like arrows that point in a certain direction on a map. They can represent a range of things like forces, velocities, or displacements.
In mathematics and physics, vectors are usually represented as bold letters, like \( \mathbf{F} \), or with an arrow above them, like \( \vec{F} \). Vectors can be visualized as having two components: a "length" or magnitude (how strong or long they are) and a "direction" (where they point).
In our exercise, the vectors represent forces, each having the same magnitude \( F \). The problems explore how different angles between these force vectors affect their summed magnitude.
Vector Addition
Adding vectors is a fundamental operation in physics, similar to adding numbers in math, but with a geometric twist. When adding two vectors, what we're actually doing is combining them to form a resultant vector that represents the combined effect of the two.
For example, if you were pushing an object with two forces, the resultant force vector shows the overall effect. To find this resultant vector, we can use several methods such as the "tip-to-tail" method, where you align the tail of one vector to the tip of another, or by breaking them into components using trigonometry.
In the context of our exercise, vector addition helps us understand how the forces combine. For part (a), when vectors are aligned in the same direction, the magnitude of their sum is maximized at \(2F\). When the forces are perpendicular as in part (b), the magnitude of the sum is \(\sqrt{2}F\), showing that the vectors influence each other differently based on the angle.
Angle Between Vectors
The angle between two vectors plays a crucial role in determining their sum. This angle can dramatically change the magnitude of the sum of the vectors, which is why it's important in situations involving forces.
The angle \(\theta\) is calculated using trigonometric relationships. For instance, when vectors are perfectly aligned (\(0^\circ\)), their effect is additive, as in part (a) with a result of \(2F\). When vectors are perpendicular (\(90^\circ\)), as shown in part (b), the cosine of the angle helps determine the resultant magnitude through the equation: \[ |mathbf{A} + \mathbf{B}| = \sqrt{A^2 + B^2} \]. Finally, when they are in opposite directions (\(180^\circ\)) in part (c), their effects cancel each other out entirely, leading to a result of zero.
Force Magnitude
Force magnitude refers to the "strength" of a force vector, measured in units such as Newtons (N). It's important to understand how this magnitude is affected by vector addition, especially in different angular scenarios.
Each force in our problem has a magnitude \(F\). When we computed the magnitude of the sum under different angles, we discovered how each configuration affects this magnitude:
  • At \(0^\circ\), the magnitude becomes \(2F\) showing they combine fully.
  • At \(90^\circ\), the magnitude was \(\sqrt{2}F\), revealing the forces partially influence each other.
  • At \(180^\circ\), the magnitude was zero, indicating complete cancellation.
Understanding these interactions highlights the relationship between directionality and magnitude in physics.

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Most popular questions from this chapter

Two forces, \(\overrightarrow{\boldsymbol{K}}_{1}\) and \(\overrightarrow{\boldsymbol{F}}_{2}\) act at a point. The magnitude of \(\overrightarrow{\boldsymbol{F}}_{1}\) is \(9.00 \mathrm{N},\) and its direction is \(60.0^{\circ}\) above the \(x\) -axis in the second quadrant. The magnitude of \(\overrightarrow{\boldsymbol{F}}_{2}\) is \(6.00 \mathrm{N},\) and its direction is \(53.1^{\circ}\) below the \(x\) -axis in the third quadrant. (a) What are the \(x\) - and \(y-\) components of the resultant force? (b) What is the magnitude of the resultant force?

A chair of mass 12.0 \(\mathrm{kg}\) is sitting on the horizontal floor; the floor is not frictionless. You push on the chair with a force \(F=40.0 \mathrm{N}\) that is directed at an angle of \(37.0^{\circ}\) below the horizontal and the chair slides along the floor. (a) Draw a clearly labeled free-body diagram for the chair. (b) Use your diagram and Newton's laws to calculate the normal force that the floor exerts on the chair.

An object with mass \(m\) initially at rest is acted on by a force \(\vec{F}=k_{1} \hat{z}+k_{2} t^{3}\) , where \(k_{1}\) and \(k_{2}\) are constants. Calculate the velocity \(\vec{v}(t)\) of the object as a function of time.

A spacecraft descends vertically near the surface of Planet X. An upward thrust of 25.0 \(\mathrm{kN}\) from its engines slows it down at a rate of \(1.20 \mathrm{m} / \mathrm{s}^{2},\) but it speeds up at a rate of 0.80 \(\mathrm{m} / \mathrm{s}^{2}\) with an upward thrust of 10.0 \(\mathrm{kN} .(\mathrm{a})\) In each case, what is the direction of the acceleration of the spacecraft? (b) Draw a free-body diagram for the spacecraft. In each case, speeding up or slowing down, what is the direction of the net force on the spacecraft? (c) Apply Newton's second law to each case, slowing down or speeding up, and use this to find the spacecraft's weight near the surface of Planet X.

A hockey puck with mass 0.160 \(\mathrm{kg}\) is at rest at the origin \((x=0)\) on the horizontal, frictionless surface of the rink. At time \(t=0\) a player applies a force of 0.250 \(\mathrm{N}\) to the puck, parallel to the \(x\) -axis; he continues to apply this force until \(t=2.00 \mathrm{s}\) . (a) What are the position and speed of the puck at \(t=2.00 \mathrm{s?}\) (b) If the same force is again applied at \(t=5.00 \mathrm{s}\) , what are position and speed of the puck at \(t=7.00 \mathrm{s} ?\)

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