Which statement is true about two isotopes of the same element?

a. they have the same mass number.
b. they have different numbers of protons.
c. they have different locations on the periodic table.
d. they have different numbers of neutrons.

Explain why electric current cannot exist if a current doesn't have a voltage source.

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).

An athlete is holding 24 lb of weights at a height of 6 inches above the stack as shown. to lower the weights, she applies a constant force of 5 lb to the handle. determine the velocity of the weights immediately before they hit the stack.