Labs

1) The Rotational and Translational KE lab asked two questions that received a large number of incorrect answers.

1) Would the velocity be affected if the mass of the ball changed. The correct answer is no, because both the KE and PE are proportional to the mass so that increasing the mass would increase the PE converted to KE sufficiently to keep v the same, or in equations

.7M vfinal^2 = Mg h initial

3) What would be the velocity if the ball just slid without friction instead of rolled. Since the final KE would still equal the initial PE we have PEi =.7Mvroll^2 = 0.5Mvslide^2

so vslide^2 = .7/.5 vroll^2 or

vslide = sqrt(.7/.5) vroll