Physics Forces and Tension Quiz

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Questions and Answers

In Figure 4, if the angle α is increased, what will happen to the tension in cable AB?

  • The tension in cable AB will decrease.
  • The tension in cable AB will remain the same.
  • The tension in cable AB will increase. (correct)
  • The tension in cable AB will become zero.

In Figure 5, if the man wants to make the crate move to the left, what must he do to the angle of the rope?

  • Keep the angle of the rope the same.
  • It is impossible to make the crate move to the left.
  • Increase the angle of the rope.
  • Decrease the angle of the rope. (correct)

In Figure 6, if the magnitude of force P is doubled, what will happen to the magnitude of force W?

  • The magnitude of force W will double.
  • The magnitude of force W will become zero.
  • The magnitude of force W will remain the same. (correct)
  • The magnitude of force W will be halved.

In Figure 8, to achieve a resultant force R which passes through point A, what changes should be made to the forces exerted by the tugboats?

<p>Change the direction of the force at point B. (D)</p> Signup and view all the answers

In Figure 9, what is the direction of the resultant force at point A, measured counter-clockwise from the positive x-axis?

<p>105 degrees (C)</p> Signup and view all the answers

In Figure 10, if the magnitude of force F1 is increased, what effect will it have on the magnitude of force F3 required for a resultant force of 20 N?

<p>The magnitude of force F3 will decrease. (D)</p> Signup and view all the answers

In Figure 11, what is the tension in the rope AB if the angle alpha is increased to 30 degrees?

<p>The tension increases. (C)</p> Signup and view all the answers

In Figure 3, if the force F2 is removed, what will happen to the magnitude of the equivalent force that replaces the three forces acting on the bracket?

<p>The magnitude of the equivalent force will decrease. (D)</p> Signup and view all the answers

What is the main difference between the scalar and vector approach to calculating moments?

<p>The scalar approach uses a single value to represent the moment, while the vector approach uses a vector with both magnitude and direction. (B)</p> Signup and view all the answers

Which of the following is NOT a factor considered when calculating the moment of a force using the vector approach?

<p>The angle between the force and the moment arm (B)</p> Signup and view all the answers

What is the moment arm, 'd', in the scalar approach to calculating moment?

<p>The perpendicular distance between the line of action of the force and the moment center (D)</p> Signup and view all the answers

In the vector approach, how are the components of the resultant moment calculated?

<p>By multiplying the position vector of the point of application of the force by the components of the force (B)</p> Signup and view all the answers

Which of the following is a suitable application for the scalar approach to calculating moments?

<p>Determining the moment of a force acting on a lever (C)</p> Signup and view all the answers

Which of the following scenarios would typically require the vector approach to calculating moments?

<p>Calculating the moment created by a force acting at an angle to a rigid body (B)</p> Signup and view all the answers

What is the main advantage of using the vector approach to calculate moments?

<p>It provides a more complete understanding of the moment, including both magnitude and direction. (C)</p> Signup and view all the answers

Which of the following is NOT a true statement about moments?

<p>The moment of a force is independent of the point of application of the force. (A)</p> Signup and view all the answers

Which of the following is NOT a true statement about the principle of moments?

<p>The principle of moments states that the moment of a force can be calculated by taking the cross product of the position vector from the moment center to the point of application of the force and the force vector. (A)</p> Signup and view all the answers

Which of the following is NOT a true statement about the moment of a force?

<p>The moment of a force is independent of the point of application of the force. (B)</p> Signup and view all the answers

What is the moment of a force about a point if the force is applied at the moment center?

<p>Zero (B)</p> Signup and view all the answers

What is the relationship between the moment of a force and the perpendicular distance from the moment center to the line of action of the force?

<p>They are directly proportional. (B)</p> Signup and view all the answers

Which of the following factors influences the magnitude of the moment of a force?

<p>All of the above (D)</p> Signup and view all the answers

What does the right-hand rule determine in the context of moments?

<p>The direction of the moment (A)</p> Signup and view all the answers

What is the principle of transmissibility in rigid body mechanics?

<p>A force can be moved along its line of action without changing its effect on the rigid body. (A)</p> Signup and view all the answers

Why is the force treated as a sliding vector when calculating the moment?

<p>Because the perpendicular distance 'd' is always measured from the moment center to the line of action of the force. (A)</p> Signup and view all the answers

What is the calculated moment of the force about point C when a 1.5 kN force is directed along the centerline of connecting rod AB?

<p>-131.99 Nm (C)</p> Signup and view all the answers

In the example involving a crowbar, what force is being applied to determine the moment about point O?

<p>60 N (C)</p> Signup and view all the answers

When calculating moments, which factor does NOT directly affect the moment about a point?

<p>Type of support used (D)</p> Signup and view all the answers

What method is suggested for expressing vectors when multiplying them?

<p>In components arranged in a matrix (A)</p> Signup and view all the answers

If the direction of the 1.5 kN force changes to exert at B, parallel to the centerline AC, how would the moment about point C be affected?

<p>It becomes zero (B)</p> Signup and view all the answers

What is the expression for the moment of a force represented in terms of the vectors r and F?

<p>MO = r × F (A)</p> Signup and view all the answers

Which matrix represents the determinant used to calculate the moment of a force?

<p>|| x y z || || Fz Fy Fx || (A)</p> Signup and view all the answers

In the expression for moment MO, what does the term (yFz - zFy) correspond to?

<p>Component along the i direction (C)</p> Signup and view all the answers

When calculating the moment using vector components, which operation is primarily used?

<p>Multiplication of vectors (C)</p> Signup and view all the answers

Which of the following correctly describes how the moment of a force is expressed mathematically?

<p>MO = (yFz - zFy)i - (xFz - zFx)j + (xFy - yFx)k (B)</p> Signup and view all the answers

What is the direction of the moment $M_C$ calculated from point C?

<p>In the direction of vector components given (D)</p> Signup and view all the answers

What is the formula used to calculate the moment of a force about a point?

<p>$M_C = rA/C \times F$ (C)</p> Signup and view all the answers

What is the calculated magnitude of the moment $M_C$?

<p>$927.64 Nm$ (C)</p> Signup and view all the answers

Which of the following statements about vector force $F$ is true?

<p>$F$ has components in all three spatial directions. (D)</p> Signup and view all the answers

What is the expression for the perpendicular distance $d$ in the moment calculation?

<p>$d = \frac{M_C}{F}$ (B)</p> Signup and view all the answers

What is the first step in calculating the moment $M_C$?

<p>Finding vector $r_{A/C}$ (A)</p> Signup and view all the answers

What is the vector expression for $rA/C$?

<p>$(-2 mi) + (4j) + (0k)$ (A)</p> Signup and view all the answers

Which component of force $F$ has the largest magnitude in the calculated vector?

<p>j-component (C)</p> Signup and view all the answers

What is the effect of increasing the tension on the cable attached at A?

<p>It increases the moment around point C. (B)</p> Signup and view all the answers

What role does the rigid mast play in the mechanics described?

<p>It acts as a pivot point. (D)</p> Signup and view all the answers

Flashcards

Maximum allowable tension

The highest force that a rope can safely handle, measured in Newtons.

Resolution of forces

Breaking down a single force into its components along different axes.

Moment of a force

The tendency of a force to cause rotation about a point, calculated using Mo = r × F.

Moment center

The point about which the moment of a force is calculated.

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Right hand rule

A method to determine the direction of a moment or torque using your right hand.

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Principle of Moments

States that the total moment about a point is the sum of the individual moments from concurrent forces.

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Force line of action

An imaginary line along which a force acts, defining how it will influence a body.

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Transmissibility principle

Forces can be moved along their line of action without changing their effect on an object.

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Resultant Force (FR)

The total force resulting from the vector addition of individual forces F1, F2, and F3.

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Equivalent Force

A single force that has the same effect as a group of forces acting together.

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Angle α

The minimum angle required for a force system to prevent exceeding a tension limit in cables.

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Force on Crate

A force that must overcome the weight of a crate for it to slide horizontally.

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Resultant of Tugboats

The combined force exerted by multiple tugboats on a barge, requiring vector addition.

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Force System with Winches

The combined force vectors from the winches acting on an object (wrecked truck).

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Magnitude of Force (F3)

The size of force F3 required to achieve a specific resultant force.

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Tension in Rope (AB)

The force in the rope suspending a box on a smooth surface, dependent on angle α.

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Scalar Approach

Calculating moment using only magnitudes of force and distance (d).

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Moment Arm (d)

The perpendicular distance from the line of action of a force to the moment center.

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Sense of the Moment

The direction of rotation caused by the force, determined by inspection.

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Vector Approach

Calculating moment by multiplying position vector with force components for resultant moment.

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Resultant Moment

The total moment created by all forces acting at a point, summed vectorially.

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Force Components (Fx, Fy, Fz)

The projections of a force acting in the x, y, and z directions.

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Perpendicular Distance

The shortest distance from a line of action to the axis of rotation.

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Calculating Moments

Determining the tendency of a force to cause rotation about a point using Mo = r × F.

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Force Direction

The orientation in which a force is applied, affecting the resulting moment.

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Force Matrix

A method of expressing forces in components arranged in a matrix for calculations.

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Moment About C

The calculated effect of a force about point C, considering the position of application.

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Crowbar Example

Using a crowbar to calculate the moment exerted by a force at contact point O.

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Moment of a force (MO)

MO is calculated using the cross product of position vector r and force vector F, expressed as MO = r × F.

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Components of Moment

The moment MO can be expressed in terms of its components: MO = Mxi + Myj + Mzk.

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Determinant in Moments

The moment components are calculated using determinants from the matrix of position and force vectors.

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Moment calculation formula

For position vector r and force F, the moments are calculated as: MO = (yFz - zFy)i - (xFz - zFx)j + (xFy - yFx)k.

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Vector multiplication

In calculating moments, vectors are multiplied to determine their effect in force systems.

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Moment calculation

The process of determining the moment of a force about a point, calculated using M = r × F.

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Position vector (rA/C)

The vector from point A to point C, used to determine the moment's arm.

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Force components

The parts of a force represented along the coordinate axes, such as i, j, and k.

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Force vector (F)

The representation of a force in vector form, showing magnitude and direction.

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Moment about point C

The total moment calculated about point C based on applied forces.

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Perpendicular distance (d)

The shortest distance from the line of action of a force to the point of rotation.

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Units of moment

The SI unit for moment is Newton-meter (Nm), a product of force and distance.

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Force application example

A scenario demonstrating forces acting on a structure, such as a tension force in a cable.

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Calculating resultant forces

The process of adding all force vectors to find a single equivalent force.

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Study Notes

Assignment I - Mechanics

  • Problem 1: Calculate the resultant force (FR) of F1, F2, and F3, and specify its direction from the x-axis.
  • Problem 2: Determine P and Q for three forces to be equivalent to R=85i+20j kN.
  • Problem 3: Replace three forces acting on a bracket (Figure 3) with a single equivalent force.
  • Problem 4: A 400 N engine block is suspended by cables AB and AC. Determine the smallest acceptable angle (α) to prevent cable tension exceeding 400 N.

Problem 5 Forces and Moments

  • Problem 5: A 200 N crate is to slide to the right. The horizontal force needed is 0.3 times the crate's weight. Calculate the force exerted on the rope for different cases in Figure 5.

Problem 6 Forces and Moments

  • Problem 6: A person applies a 250 N force (P) to a wheelbarrow. The resultant force (R) is 50i. Determine the force (W) exerted on the wheelbarrow.

Problem 7 Forces and Moments

  • Problem 7: Replace three forces (T1, T2, and T3) acting on a flagpole with a single, equivalent force. Given: T1 = 1000 N, T2 = 2000 N, T3 = 1750 N.

Problem 8 Forces and Moments

  • Problem 8: Determine the resultant force (R) of three tugboats maneuvering a barge. Specify the point on the x-axis through which R passes.

Problem 9 Forces and Moments

  • Problem 9: Two cables pull on a wrecked truck (Figure 8). Calculate the magnitude and direction of the resultant force at point A. Given: Tension in cable AB is 10 kN and tension in cable AC is 7.5 kN.

Problem 10 Forces and Moments

  • Problem 10: Determine the magnitude and direction of the smallest force F3, such that the resultant of all three forces has a magnitude of 20N.

Problem 11 Forces and Moments

  • Problem 11: A 600 N box is held in place on a truck bed. Find the tension in the rope (AB) for a given angle (α =25°). What is the maximum allowable value of a if the maximum allowable tension is 400 N?

Problem 12 Forces and Moments

  • Problem 12: Resolve a 250 N force (Figure 12) into components along the u and v axes. Calculate the magnitude of these components.

Forces and Moments – Additional Theory

  • Forces Cause Two Types of Motion: Forces cause translational and rotational motion in rigid bodies.
  • Moment of a Force: The tendency of a force to rotate a body is called its moment.
  • Moment Centre: A moment may occur about a point, the moment centre.
  • Scalar Approach to Moment: Moment = force × perpendicular distance between force line of action and moment centre.
  • Vector Approach to Moment: Moment = position vector × force vector.
    • Components of force must be known to use vector approach .
  • Principle of Moments (Varignon's Theorem): The moment of a resultant force is equal to the sum of moments of its components.

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