A cylinder rolls down a hill of height h. What is the speed of the center of mas

Practice Questions

Q1
A cylinder rolls down a hill of height h. What is the speed of the center of mass when it reaches the bottom?
  1. √(2gh)
  2. √(3gh)
  3. √(4gh)
  4. √(5gh)

Questions & Step-by-Step Solutions

A cylinder rolls down a hill of height h. What is the speed of the center of mass when it reaches the bottom?
  • Step 1: Identify the height of the hill as 'h' and the mass of the cylinder as 'm'.
  • Step 2: Understand that at the top of the hill, the cylinder has potential energy given by the formula PE = mgh.
  • Step 3: When the cylinder rolls down, this potential energy converts into kinetic energy.
  • Step 4: The total kinetic energy (KE) at the bottom consists of two parts: translational kinetic energy (1/2 mv^2) and rotational kinetic energy (1/2 Iω^2).
  • Step 5: For a solid cylinder, the moment of inertia (I) is (1/2)mR^2, where R is the radius of the cylinder.
  • Step 6: The relationship between linear speed (v) and angular speed (ω) for rolling without slipping is ω = v/R.
  • Step 7: Substitute I and ω into the kinetic energy formula: KE = 1/2 mv^2 + 1/2 (1/2)mR^2(v/R)^2.
  • Step 8: Simplify the equation to combine terms: KE = 1/2 mv^2 + 1/4 mv^2 = (3/4)mv^2.
  • Step 9: Set the potential energy equal to the total kinetic energy: mgh = (3/4)mv^2.
  • Step 10: Cancel 'm' from both sides and solve for v: gh = (3/4)v^2, leading to v^2 = (4/3)gh.
  • Step 11: Take the square root to find the speed: v = √(4/3)√(gh) = √(3gh).
  • Conservation of Energy – The principle that the total energy in a closed system remains constant, allowing potential energy to convert into kinetic energy.
  • Moment of Inertia – A measure of an object's resistance to changes in its rotation, crucial for calculating the kinetic energy of rolling objects.
  • Rolling Motion – The combination of translational and rotational motion, where the relationship between linear velocity and angular velocity is defined.
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