Which is a good example of a contact force? A. protons in the nucleus of an atom B. a ball falling down after it's thrown up into the air C. a satellite orbiting Earth D. a bat hitting a ball

The chart shows the bid provided by four contractors to complete a job. which contractor is the most cost-effective?

Modern pennies are composed of zinc coated with copper. a student determines the mass of a penny to be 2.482 g and then makes several scratches in the copper coaling (to expose the underlying zinc). the student puts the scratched penny in hydrochloric acid, where the following reaction occurs between the zinc and the hcl (the copper remains undissolved): zn(s) + 2 hcl(aq) → h2(g) + zncl(aq)the student collects the hydrogen produced over water at 25 °c. the collected gas occupies a volume of 0.899 l at a total pressure of 79 j mmhg. calculate the percent zinc (by mass) in the penny. (assume that all the zn in the penny dissolves.)

What metric units would you use to measure the thickness of a key