What number should be substituted for the question mark to balance the equation and why is that the correct number? 2c4h10 +? o2 → 8co2 + 10h2o + heat a. the number 8 is needed to balance the equation. the right side of the equation shows 16 oxygen atoms, so the left side needs 8 × o2. b. the number 9 is needed to balance the equation. the right side shows 8 oxygen atoms in carbon dioxide and 10 oxygen atoms in water for a total of 18 oxygen atoms. c. the number 13 is needed to balance the equation. the right side of the equation shows 26 oxygen atoms, so the left side needs 13 × o2. d. the number 5 is needed to balance the equation. the right side shows 10 oxygen atoms, so the left side needs 5 oxygen atoms.

World class speed skaters can skate a 3,000-m course in about 4 minutes.what is their average speed for this course? a. 12.5 m/sb. 1.33 m/sc. 1.25 m/sd. 13.3 m/s

3. a worker pushes a 30.5 kg polished stone along a polished table with a force on bonin a straight line for 5.20 s after starting from rest. there is no friction between thestone and the table. at the end of the table. the stone is hooked to a cable with a lengthof 62.0 cm to rotate it to a rough table to store until they can be picked up. the roughtable has a coefficient of static friction 0.702 with the polished stone. remember that 8= 9.80 m/s2a) what is the speed of the stone when it is hooked to the cable? b) what is the tension in the cable while the stone is rotating? (there is still nofriction)c) how much force is needed to make the stone begin sliding from rest on therough table? ius = 0.70262.0 cm30.5 kg20.5 kg6= 0

Which of the following examples illustrates static friction? a box sits stationary on a ramp. a ball rolling on the lawn eventually comes to rest. a car rounds a curve on a road. a fish swims upstream.