Kinematics and Motion

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Questions and Answers

Consider a projectile launched with initial velocity $v_0$ at an angle $\theta$ with respect to the horizontal. Accounting for air resistance, which is proportional to the square of the velocity, what is the qualitative effect on the range and maximum height compared to the ideal projectile motion without air resistance?

  • Range decreases, maximum height increases.
  • Range increases, maximum height decreases.
  • Both range and maximum height increase.
  • Both range and maximum height decrease. (correct)

A particle's position is given by $r(t) = (At^3 + Bt)i + (Ct^2 + Dt^4)j$, where A, B, C, and D are non-zero constants. Determine the conditions under which the particle's acceleration will have only a j-component at a specific time $t_0$.

  • $6At_0 = 0$ and $2C + 12Dt_0^2 \neq 0$ (correct)
  • $6At_0 \neq 0$ and $2C + 12Dt_0^2 = 0$
  • $6At_0 \neq 0$ and $2C + 12Dt_0^2 \neq 0$
  • $6At_0 = 0$ and $2C + 12Dt_0^2 = 0$

A block of mass $m_1$ rests on a horizontal, frictionless surface and is connected to a hanging mass $m_2$ by a massless string over a massless, frictionless pulley. Determine the Lagrangian for this system in terms of the horizontal displacement $x$ of $m_1$.

  • $L = \frac{1}{2}(m_1 + m_2)\dot{x}^2 - m_2gx$
  • $L = \frac{1}{2}m_1\dot{x}^2 - m_2gx$
  • $L = \frac{1}{2}(m_1 + m_2)\dot{x}^2 + m_2gx$ (correct)
  • $L = \frac{1}{2}m_1\dot{x}^2 + m_2gx$

Consider an Atwood machine with two masses, $m_1$ and $m_2$, connected by a massless string over a pulley with moment of inertia $I$ and radius $R$. Derive the equation of motion for the system using the Euler-Lagrange equation, expressed in terms of the angular acceleration $\alpha$ of the pulley.

<p>$(m_1 + m_2 + \frac{I}{R^2})R\alpha = (m_1 - m_2)g$ (B)</p> Signup and view all the answers

A projectile is launched on a planet with no atmosphere but a non-uniform gravitational field described by $g(y) = g_0e^{-ky}$, where $g_0$ is the gravitational acceleration at the surface (y=0) and k is a positive constant. Determine a modified expression for the maximum height reached by the projectile, assuming the initial vertical velocity component is v_y0.

<p>$H = \frac{1}{k} \ln(1 + \frac{kv_{y0}^2}{2g_0})$ (C)</p> Signup and view all the answers

Two blocks, $m_1$ and $m_2$ ($m_1 > m_2$), are connected by a string that passes over a pulley. Considering the effects of a non-ideal, massive pulley with radius $R$ and moment of inertia $I$, along with friction in the pulley's axle (modeled as a torque $\tau$), derive the expression for the acceleration of the masses.

<p>$a = \frac{(m_1 - m_2)g - \tau/R}{m_1 + m_2 + I/R^2}$ (D)</p> Signup and view all the answers

A vehicle moving at an initial velocity $v_0$ applies its brakes, resulting in a deceleration that increases linearly with time, described by $a(t) = -kt$, where k is a positive constant. Determine the time at which the vehicle comes to a complete stop.

<p>$t = \sqrt{\frac{2v_0}{k}}$ (D)</p> Signup and view all the answers

A projectile is launched on level ground with an initial velocity $v_0$ at an angle $\theta$. Determine an expression for the time at which the projectile's speed is minimized during its flight.

<p>$t = \frac{v_0 \sin(\theta)}{g}$ (D)</p> Signup and view all the answers

Consider a modified Atwood machine where the pulley has a non-negligible mass and radius, leading to rotational inertia $I$. If the two masses, $m_1$ and $m_2$, are released from rest, and the string does not slip on the pulley, determine the ratio of the tensions $T_1/T_2$ in the string segments connected to $m_1$ and $m_2$ respectively.

<p>$T_1/T_2 = (m_1R^2 + I) / (m_2R^2 + I)$ (C)</p> Signup and view all the answers

A ball is thrown vertically upwards with an initial velocity $v_0$ in a medium where the drag force is proportional to the velocity, i.e., $F_d = -bv$, where b is a positive constant. Determine the time it takes for the ball to reach its maximum height.

<p>$t = \frac{m}{b} \ln(1 + \frac{b v_0}{mg})$ (B)</p> Signup and view all the answers

Flashcards

What is Kinematics?

Branch of mechanics studying the motion of bodies, disregarding mass and forces.

What is Average Velocity?

Displacement (Δx) divided by the time interval (Δt) during which the displacement occurred : v = Δx/Δt.

What is Instantaneous Speed?

The magnitude of the instantaneous velocity.

Define Acceleration.

The rate of change of velocity with respect to time. a = Δv/Δt.

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What are Equations of Linear Motion?

Relates displacement, initial velocity, final velocity, acceleration, and time when acceleration is constant.

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What is Free Fall?

Motion where the only force acting on an object is gravity.

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What is Projectile Motion?

Motion of an object launched into the air, subject to gravity.

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What are Newton's Laws of Motion?

Statements describing the relationships between force, mass, and motion.

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What is the Atwood Machine?

A device with a pulley and two masses connected by a string, to demonstrate motion principles.

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Study Notes

  • Kinematics and Newton's laws of motion are key topics.

Kinematics

  • Concerned with the motion of bodies.
  • Does not consider the masses of bodies or forces causing motion.

Average Velocity and Average Speed

  • For a particle with displacement Δx during a time interval Δt, average velocity is v = Δx/Δt = (x₂ - x₁)/(t₂ - t₁)

Instantaneous Velocity and Speed

  • Instantaneous speed equals the magnitude of instantaneous velocity.

Acceleration

  • An object accelerates if its velocity changes with time.
  • Average acceleration is a = Δv/Δt = (v₂ - v₁)/(t₂ - t₁)
  • Instantaneous acceleration is a = lim(Δt→0) Δv/Δt

Equations of Linear Motion Under Constant Acceleration

  • Also known as Newton's equations of motion.

Free Fall

  • Topics include calculating initial speed for a given maximum height and the time a ball is in the air.
  • Also covers the time it takes for a ball to strike the ground with a given initial speed and height.
  • Includes calculating the time to reach max altitude, max altitude, velocity, and acceleration of a vertically thrown ball.

Motion in 2 Dimensions – Projectile Motion

  • Considers motion in horizontal and vertical directions.
  • Horizontal velocity component: Ux = U cos θ
  • Vertical velocity component: Uy = U sin θ
  • Horizontal acceleration: ax = 0
  • Vertical acceleration: ay = g (or – g), depends on trajectory direction.
  • Maximum height H = (v²-u²)/2g = (u²sin² θ)/2g
  • Total time of flight: T = (2u sin θ)/g
  • Horizontal distance (range): Sx = (u cos θ) * (2u sin θ)/g = (u² sin 2θ)/g
  • Maximum horizontal range occurs when R = (u² sin 2θ)/g.
  • For a projectile released from a height, the following equations can be easily derived
    • H = 1/2gt²
    • R = ut
    • t= √2H/g

Newton's Laws of Motion

  • Dynamics deals with the description of motion while considering its causes and the masses of bodies involved.
  • The relationship between vector quantities (displacement, acceleration, velocity) with force and mass comprise the statements known as Newton's laws of motion.

Atwood Machine

  • A device demonstrating dynamics principles, using a string, pulley, and two masses.
  • Tension is constant throughout the string.
  • Acceleration of two masses (m1 and m2, m1 > m2): a = g * (m1 - m2) / (m1 + m2)
  • Potential lab use: determining acceleration due to gravity, assuming a massless, frictionless system.

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