Question

Consider 2 bicycle riders- A and B. The 2 riders, their bikes, and the wheels of their bikes all have equal mass. The radii of the wheels are both equal, however the wheels of the bike A have most of their mass at the rims while the wheels of bike B have their mass spread "evenly" over the whole area the wheel. The two cyclists travel at the same speed on level ground and approach a low hill. If they coast up the hill (rather than peddling) which bike will have a larger speed?

a) They will have the same speed

b) Bike A

c) Bike B

JUSTIFY YOUR ANSWER.... IN WORDS PLEASE AND NOT MATH!!!! thank you

Answer 1

Moment of inertia (MI) of a rotating object is the tendency of resistance against the rotational motion. More moment of inertia means it takes more energy to keep the object accelerating than an object with lesser moment of inertia.

A wheel with most of the mass at its perimeter have twice MI than a wheel with with same mass and even mass distribution. So at the same speed a "Ring"(Bike A) possess more rotational energy than a "disk"(Bike B).

At same speed bike A has more rotational energy in it than B. While coasting up they'll start to loose this rotational energy as they gain potential energy. As A has more initial rotational energy than B, so A will have larger speed as they go up and start to loose energy at a slower rate.

Option B is correct.