A rod XY 12m long balances horizontally when pivoted at 5.5 m from the end X. when a weight 120 N is suspended at 3 m from the end Y, the rod
balance horizontally on a knife edge placed at 7.5 m from the end X. what is
the mass of the rod.

Most short-period comets do not have randomly oriented orbits because

The number of passengers who arrive at the platform of a subway station for the 10 am train is a random variable with a mean of 120 and a variance of 16. find the lower bound of the probability that there will be between 100 and 140 passengers (round off to second decimal place).

Metals are good conductors of electricity because they