During a laboratory session

PHYSICS · Subjective · A Level · Physics · Engineering physics · Engineering physics

Problem

During a laboratory session, a student tried to calculate the kinetic energy of a fly-wheel. The moment of inertia of the wheel about its axis is

I = 2.0\,\text{kg}\,\text{m}^{2}

. The wheel was observed to rotate at

600\,\text{rpm}

. The student’s working is reproduced below: Step 1:

\omega = 600\times2\pi = 1200\pi\,\text{rad}\,\text{s}^{-1}

Step 2:

K = \tfrac{1}{2}\,I\,\omega

Step 3:

K = 0.5\times2.0\times1200\pi = 1200\pi\,\text{J}

Answer the following questions: (a) Identify every dimensional or unit-related error present in Steps 1–3. For each error, state the correct conversion or formula that should have been used. (b) Redo the entire calculation with the correct angular speed and the correct kinetic-energy formula, obtaining the numerical value of

K

in joule. (c) State how dimensional checking at each step would have alerted the student before arriving at the wrong answer.

Related theory

Browse the problem library