Dynamics Chapter 15 Flashcards

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Questions and Answers

The linear impulse and momentum equation is obtained by integrating the ______ with respect to time.

equation of motion

Which parameter is not involved in the linear impulse and momentum equation? (Select one option)

  • Velocity
  • Displacement (correct)
  • Force
  • Time

Calculate the impulse due to the force. (Select one option)

  • 15 N·s
  • 20 kg·m/s
  • 5 N·s
  • 10 kg·m/s (correct)

Determine the force F if the particle's mass is 2 kg. (Select one option)

<p>(20 i +17.3 j) N (C)</p> Signup and view all the answers

Determine the net impulse on the aircraft over t = 10 s. (Select one option)

<p>0 kN·s (A)</p> Signup and view all the answers

Determine the net impulse on the cabinet during this time interval. (Select one option)

<p>100 lb·s (A)</p> Signup and view all the answers

The internal impulses acting on a system of particles always __________.

<p>sum to zero</p> Signup and view all the answers

Weight is a/an __________ during impulse-momentum analysis.

<p>non-impulsive force</p> Signup and view all the answers

Over the short time span of a tennis ball hitting the racket, the ball's weight can be considered _____________.

<p>non-impulsive</p> Signup and view all the answers

How many impulsive forces act on the drill rod during drilling? (Select one option)

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

What is the velocity of the block immediately after impact? (Select one option)

<p>75 m/s (A)</p> Signup and view all the answers

During the impact with the bat, how many impulses of importance are used to find the final velocity of the ball? (Select one option)

<p>One (A)</p> Signup and view all the answers

When the motion of one or both particles is at an angle to the line of impact, the impact is said to be ________.

<p>oblique impact</p> Signup and view all the answers

The ratio of the restitution impulse to the deformation impulse is called ________.

<p>restitution coefficient</p> Signup and view all the answers

Can one of the balls leave the impact with a kinetic energy greater than before the impact? (Select one option)

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

Under what condition is the energy lost during a collision maximum? (Select one option)

<p>e = 0.0 (A)</p> Signup and view all the answers

If the velocity of block A after the collision is 4 m/s, what is (vB)2? (Select one option)

<p>2 m/s ← (A), 2 m/s ← (B)</p> Signup and view all the answers

If e = 0.8, (vx) 2 is _____ after the collision. (Select one option)

<p>less than (vx) 1 (C)</p> Signup and view all the answers

Select the correct expression for the angular momentum of a particle about a point.

<p>r × (m v)</p> Signup and view all the answers

The sum of the moments of all external forces acting on a particle is equal to what? (Select one option)

<p>Time rate of change of angular momentum (B)</p> Signup and view all the answers

If a particle moves in the x - y plane, its angular momentum vector is in the? (Select one option)

<p>z direction (A)</p> Signup and view all the answers

If there are no external impulses acting on a particle, what can be said about momentum conservation? (Select one option)

<p>Both linear momentum and angular momentum are conserved (D)</p> Signup and view all the answers

Which of the following principles can be applied to solve for the velocity of the ball when r = 2 ft? (Select one option)

<p>None of the above (D)</p> Signup and view all the answers

If a particle moves in the z - y plane, its angular momentum vector is in the? (Select one option)

<p>x direction (A)</p> Signup and view all the answers

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Study Notes

Equation of Motion

  • Linear impulse and momentum equation is derived by integrating the friction force over time.
  • Displacement is not a parameter in the linear impulse and momentum equation, while velocity, time, and force are involved.

Impulse Calculations

  • Impulse due to a force can be calculated using the area under the force-time curve. For example, a force of 10 N applied for 1 second yields an impulse of 10 kg·m/s.
  • If a constant vertical force of 981 kN is exerted on an aircraft hovering for 10 seconds, the net impulse is 0 kN·s, as the initial and final velocities are the same.

Forces and Impulses

  • Internal impulses acting on a particle system always sum to zero.
  • Weight can generally be considered a non-impulsive force during short interactions due to its negligible effect on momentum change.
  • The impact force on a drill rod during drilling involves two impulsive forces, neglecting the rod's weight.

Collision Dynamics

  • When a bullet embeds into a block, the block's velocity can be calculated using conservation of momentum principles; for example, a 20 g bullet at 1200 m/s results in a block velocity of 75 m/s post-impact.
  • During a baseball bat impact, one significant impulse determines the final velocity of the ball.

Coefficient of Restitution

  • The restitution coefficient relates the restitution impulse to the deformation impulse in a collision.
  • A coefficient of restitution of 0.79 implies that one ball may leave a collision with greater kinetic energy than before.
  • Maximum energy loss in a collision occurs when the coefficient of restitution (e) is 0.0, indicating a perfectly inelastic collision.

Angular Momentum

  • Angular momentum of a particle about a point is calculated as ( r \times (m v) ).
  • If external impulses are absent, both linear momentum and angular momentum are conserved.
  • The vector direction of angular momentum for particles in the x-y plane is along the z direction.

Motion Transformation

  • The time rate of change of angular momentum is equivalent to the sum of the moments of all external forces acting on a particle.
  • If a particle moves in the z-y plane, its angular momentum vector is aligned with the x direction.

Miscellaneous Principles

  • In a scenario where a ball moves in a circular path while a cord is pulled down, principles of energy, linear momentum, or mass conservation do not apply in calculating the ball's new velocity.

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