Running head: TEXTBOOK EXERCISES
November 4, 2013
20. Suppose that the three balls shown in Exercise 19 start simultaneously from the tops of the
hills. Which one reaches the bottom first? Explain.
The ball in the middle will reach the bottom first. It starts off with faster acceleration so it has
more speed than the other two.
22. Which is greater, an acceleration from 25 km/h to 30 km/h or one from 96 km/h to 100 km/h
if both occur during the same time?
Acceleration from 25 km/h to 30 km/h is 5 and 96 km/h to 100km/h is only 4. The greater
acceleration is 25 km/h to 30 km/h.
14. Gravity on the surface of the Moon is only 1/6 as strong as gravity on Earth. What is the
weight of a 10-kg object on the Moon and on Earth? What is its mass on each?
The mass of an object does not change, only the weight changes. The mass of a 10-kg object on
both the Moon and on Earth is 10-kg.
W = mg
G on Earth =
G on Moon = (1/6) (9.8 m/s^2) = 1.63 m/s^2
Earth: W = (9.8) (10 kg) = 98 N
Moon: W = (1.63) (10) = 16.3 N
18. A grocery bag can withstand 300 N of force before it rips apart. How many kilograms of
apple can it safely hold?
F = ma
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