What makes simple machines useful for people without enough strength to complete a task? a. work is reduced, while time is decreased. b. input force is reduced, while time is increased. c. power is increased, while distance is decreased. d. input force is reduced, while distance is increased.

Which are advantages of renewable resources? check all that apply. renewable energy supplies are completely reliable everywhere. some renewable resources will never be used up. little or no waste is produced by renewable resource plants. electricity can be generated in large quantities. many renewable energy facilities have lower operating costs.

The smallest particle of an element that retains its identity in a chemical reaction. true or false

The radioactive isotope of lead, pb-209, decays at a rate proportional to the amount present at time t and has a half-life of 3.3 hours. if 1 gram of this isotope is present initially, how long will it take for 80% of the lead to decay? (round your answer to two decimal places.)