Kinematics and Newton's Laws of Motion

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Questions and Answers

A particle's position is given by $x(t) = At^3 - Bt$, where $A$ and $B$ are constants. Determine the condition for the particle's acceleration to be zero.

  • $t = \sqrt{B/(6A)}$ (correct)
  • $t = \sqrt{B/(3A)}$
  • $t = \sqrt{2B/(3A)}$
  • $t = \sqrt{A/(6B)}$

A projectile is launched at an angle $\theta$ with an initial velocity $v_0$. Assuming negligible air resistance, what angle maximizes the range of the projectile over level ground?

  • $\theta = \arctan{(1/2)}$
  • $\theta = 30^\circ$
  • $\theta = 45^\circ$ (correct)
  • $\theta = 60^\circ$

A car accelerates from rest with a constant acceleration $a$ for a time $t_1$. It then decelerates at a constant rate $-b$ until it comes to rest. What is the total time elapsed?

  • $t_1(a+b)/a$
  • $t_1(a/b)$
  • $t_1(a+b)/b$ (correct)
  • $t_1(b/a)$

A block of mass $m$ is released from rest on an inclined plane with an angle $\theta$. If the coefficient of kinetic friction is $\mu_k$, determine the velocity of the block after it has traveled a distance $d$ along the incline.

<p>$\sqrt{2gd(\sin{\theta} - \mu_k\cos{\theta})}$ (B)</p> Signup and view all the answers

An Atwood machine consists of two masses, $m_1$ and $m_2$, connected by a string over a pulley. Assuming a massless string and pulley, derive an expression for the tension $T$ in the string.

<p>$T = (2m_1m_2g) / (m_1 + m_2)$ (C)</p> Signup and view all the answers

A ball is thrown vertically upwards with an initial velocity $v_0$ from the top of a building of height $h$. Find the time it takes for the ball to reach the ground.

<p>$(v_0 + \sqrt{v_0^2 + 2gh}) / g$ (D)</p> Signup and view all the answers

Two blocks, $A$ and $B$, with masses $m_A$ and $m_B$ respectively, are connected by a light string over a frictionless pulley. Block $A$ is on a horizontal surface with coefficient of kinetic friction $\mu_k$, and block $B$ hangs vertically. Find the acceleration of the system.

<p>$g(m_B - \mu_k m_A) / (m_A + m_B)$ (A)</p> Signup and view all the answers

A particle moves along the x-axis with a velocity given by $v(t) = v_0e^{-kt}$, where $v_0$ and $k$ are positive constants. Determine the total distance the particle travels before coming to rest.

<p>$v_0 / k$ (C)</p> Signup and view all the answers

A projectile is launched with initial velocity $v_0$ at an angle of $\theta$ above the horizontal from a height $h$ above the ground. Find an expression for the horizontal range of the projectile.

<p>$\frac{v_0 \cos(\theta)}{g} \left(v_0 \sin(\theta) + \sqrt{v_0^2 \sin^2(\theta) + 2gh}\right)$ (B)</p> Signup and view all the answers

A car is traveling at a constant speed $v$ on a circular track of radius $r$. What is the minimum coefficient of static friction $\mu_s$ required for the car not to slip?

<p>$v^2 / (gr)$ (A)</p> Signup and view all the answers

A projectile is fired upwards at an angle of 60 degrees to the horizontal with an initial velocity of 20 m/s. At the highest point of its motion, what is its velocity?

<p>10 m/s (D)</p> Signup and view all the answers

An object is dropped from a height $h$ above the earth. If air resistance is proportional to the velocity ($F = -bv$), what is the terminal velocity of the object?

<p>$mg/b$ (C)</p> Signup and view all the answers

A cannonball is fired at an angle of 30 degrees above the horizontal on flat ground. Assuming the cannonball lands at the same elevation from which it was fired, at what angle (greater than zero) could it be fired and still land at the same spot, assuming all other variables remain unchanged?

<p>60 degrees (D)</p> Signup and view all the answers

An elevator car has a mass of 1000 kg and is carrying passengers with a combined mass of 200 kg. If the tension in the cable is 15000 N, what is the acceleration of the elevator?

<p>2.75 m/s^2 upwards (B)</p> Signup and view all the answers

A small block is placed on a rotating turntable a distance $r$ from the center. If the coefficient of static friction between the block and turntable is $\mu_s$, what is the maximum speed the turntable can rotate (in rad/s) before the block slips?

<p>$\sqrt{\mu_s g / r}$ (C)</p> Signup and view all the answers

A rocket is launched vertically upwards from rest. If the rocket engine provides a constant upward thrust $F$ and the rocket has a mass $m$, what is the velocity of the rocket at time $t$, assuming we ignore air resistance and gravity?

<p>$Ft/m$ (B)</p> Signup and view all the answers

A ball is thrown with an initial speed $v_0$ at an angle of $\theta$ with respect to the horizontal. Assuming no air resistance, what is the ratio of the ball's kinetic energy at its highest point to its initial kinetic energy?

<p>$(\cos{\theta})^2$ (D)</p> Signup and view all the answers

Two blocks, one with mass $m$ and the other with mass $3m$, are connected by a massless string that passes over a frictionless pulley. The blocks are released from rest. What is the magnitude of the acceleration of the block with mass $m$?

<p>$0.5g$ (D)</p> Signup and view all the answers

A car starts from rest and accelerates uniformly to a speed of 20 m/s in 5 seconds. It then maintains this speed for 10 seconds, and finally decelerates uniformly to rest in 4 seconds. What is the magnitude of the average velocity for the entire trip?

<p>14.7 m/s (A)</p> Signup and view all the answers

A projectile is launched from the ground with an initial velocity $v_0$ at an angle $\theta$ above the horizontal. At what time after launch does the projectile achieve its maximum height?

<p>$v_0 \sin(\theta) / g$ (B)</p> Signup and view all the answers

Flashcards

Kinematics

Branch of mechanics concerned with the motion of bodies, without considering the forces or masses.

Average Velocity

The change in position (displacement) of an object over a specific time interval.

Instantaneous Speed

The absolute value (magnitude) of the instantaneous velocity.

Acceleration

The rate at which velocity changes with time.

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Newton's Laws of Motion

Dynamics that describes motion while considering its causes and the masses of bodies involved.

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Atwood Machine

Device with a string, a pulley and two masses, often used to demonstrate principles of dynamics.

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Newton's Laws of Motion

The relationship between vector quantities ( displacement, acceleration, velocity) with force and mass

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Projectile Motion

The motion of an object in a curved path when thrown near the Earth's surface.

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Free fall

Vertical motion due to gravity

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Velocity

Is the rate of change of position with respect to time, measured in a specific direction.

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Study Notes

  • The topics covered are Kinematics and Newton's Laws of Motion.

Kinematics

  • It is a branch of mechanics focusing on the motion of bodies
  • Kinematics does not consider the forces or masses causing the motion

Average Velocity and Average Speed

  • Average velocity is defined for a particle undergoing displacement (∆x) over a time interval (∆t)
  • The formula for average velocity is: 𝑣 = ∆𝑥/∆𝑡 = (𝑥2 − 𝑥1)/(𝑡2 − 𝑡1)

Instantaneous Velocity and Speed

  • Instantaneous speed refers to the magnitude (absolute value) of instantaneous velocity

Acceleration

  • Acceleration occurs when an object's velocity changes with time.
  • Average acceleration is calculated as: 𝑎 = ∆𝑣/∆𝑡 = (𝑣2 − 𝑣1)/(𝑡2 − 𝑡1), where velocity changes from 𝑣1 to 𝑣2 over time interval 𝑡1 to 𝑡2
  • Instantaneous acceleration is the limit of ∆𝑣/∆𝑡 as ∆𝑡 approaches 0: 𝑎 = lim (∆𝑡→0) ∆𝑣/∆𝑡

Equations of Linear Motion

  • These equations apply under constant acceleration
  • They are also known as Newton's equations of motion

Projectile Motion

  • Horizontal motion: 𝑈𝑥 = 𝑈 cos 𝜃
  • Vertical motion: 𝑈𝑦 = 𝑈 sin 𝜃
  • Horizontal acceleration: 𝑎𝑥 = 0
  • Vertical acceleration: 𝑎𝑦 = 𝑔 (or – 𝑔, depending on direction)

Maximum Height of a Projectile

  • Vertical motion is considered to determine the maximum height (H)
  • Formula to determine max height: 𝐻 = (𝑣𝑦2 − 𝑢𝑦2)/2𝑔 = (𝑢2 sin2 𝜃)/2𝑔
  • At maximum height, the vertical component of velocity (𝑣𝑦) is 0

Total Flight Time of a Projectile

  • First determine the time to reach maximum height
  • Time to reach max height: 𝑡 = (𝑣𝑦 − 𝑢𝑦)/𝑔 = (𝑢 sin 𝜃)/𝑔
  • Total time of flight: 𝑇 = 2𝑢 sin 𝜃/𝑔

Horizontal Range of a Projectile

  • Horizontal motion is considered to determine horizontal distance (range)
  • Horizontal range formula: 𝑠𝑥 = (𝑢 cos 𝜃)⋅(2𝑢 sin 𝜃)/𝑔 = (𝑢2 sin 2𝜃)/𝑔
  • Maximum horizontal range: 𝑅 = (𝑢2 sin 2𝜃)/𝑔

Projectile Released from a Height

  • Height: 𝐻 = (1/2)⋅𝑔𝑡^2
  • Range: 𝑅 = 𝑢𝑡
  • Time: 𝑡 =sqrt(2𝐻/𝑔)

Newton's Laws of Motion

  • Dynamics, a physics branch, describes motion with causes and masses
  • Newton's Laws of Motion relate vector quantities (displacement, acceleration, velocity) with force and mass

Atwood Machine

  • Used to demonstrate dynamics principles
  • In its basic form, it includes a string, a pulley, and two masses
  • Key feature: constant tension throughout the string
  • If m1 > m2, the acceleration of the masses is: 𝑎 = 𝑔⋅(𝑚1 − 𝑚2)/(𝑚1 + 𝑚2)
  • In a lab with equal masses, the system is in equilibrium with no motion
  • Unequal masses will result in measurable acceleration, where u, s, and t are given
  • The setup determines gravity acceleration in the lab
  • The pulley and string are considered massless and the system frictionless

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