A bike racer completed a 20.0 kilometer race. She pedaled the first 5.0 kilometers with an average speed of 20.0 km/hr. She pedaled the next 5.0 kilometers (which were uphill) at an average speed of 10.0 km/hr. She completed the next 5.0 kilometers (which were downhill) at an average speed of 25.0 km/hr and the final 5.0 kilometers she covered at an average speed of 20.0 km/hour. Required:a. What was the biker's average speed for the whole race?b. How long did it take the biker to complete the race?

Why is alternating current more effective at long–distance travel than direct current? a. the power lines are made out of conductors. b. transformers increase or decrease voltage as needed. c. the ac generator is more efficient. d. ac has lower voltage than dc.

Automobile fuel efficiency is often measured in miles that the car can be driven per gallon of fuel (mpg). heavier cars tend to have lower fuel efficiencies (lower mpg ratings). which variable (weight or fuel efficiency) is most naturally considered the explanatory (predictor) variable in this context?

Because air contracts as it cools, the air pressure inside a freezer is typically lower than on the outside. why do ice cubes inside a freezer tend to shrink over time? a. the ice dissolves oxygen from the air, forming a denser crystalline matrix.b. the ice reacts chemically with carbon dioxide in the air, forming gaseous carbon compounds.c. the ice melts, and then the liquid freezes as ice crystals on the bottom of the freezer.d. the ice sublimes, and then the water vapor deposits as ice crystals on the sides of the freezer.