Download Homework 4: Chapter 5 – Questions: 2,5,7,8,9,16,18,22 and

Homework 4: Chapter 5 – Questions: 2,5,7,8,9,16,18,22 and Chapter 8 – Questions: 1,5,7,10,11,12
Chapter 5
2.
Anything that has mass will exert a gravitational force on you, so all the objects exert a force on you.
5.
E – At point E both spheres pull in the same direction, and E is very close to the larger sphere.
7.
Twice the mass causes the force to double (increase), but doubling the diameter (or radius) increases
the distance and causes the force to decrease by a factor of two squared (1/4). The net result is that
the force decreases by a factor of two (2/4 = 1/2).
8.
800 N
9.
The objects in an orbiting spacecraft are not “weightless” because the earth is still exerting a
gravitational force on them. They are, though, “apparently” weightless, meaning that they do not
feel the floor holding them up.
16. Weight is a force and mass is the quantity of matter. Weight = mass x g.
18. The moon does fall toward the earth. It wants to travel in a straight line, but the earth exerts a force
on it pulling it away from the straight path and toward the earth.
22. Mass does not change. It represents the quantity of matter in you and that doesn’t change when you
merely travel from one point to another.
Chapter 8
1.
The 50 lb upward and downward forces do no work because the direction of motion of the crate is
not in the same direction as either of the vertical forces. The 20 lb force does positive work (force
and motion are in the same direction), and the 10 lb force does negative work (force and motion are
in opposite directions).
5.
Positive work: B
Negative work: D
No work: C
7.
a. The ball has kinetic energy when first hit. As it rises, it loses kinetic energy and gains potential
energy. At the top of its arc it has no kinetic energy and all of its energy is potential energy.
b. The bungee jumper starts with gravitational potential energy. As she falls, the gravitational
potential energy changes into kinetic energy. When the bungee cord first becomes taut the jumper
has gravitational potential energy and maximum kinetic energy. As the cord stretches, the
gravitational potential energy decreases further and the kinetic energy also decreases, but the elastic
(stretching of the cord like a rubber band) potential energy increases. When the cord is fully
stretched, the gravitational potential energy and the kinetic energy are zero and the elastic potential
energy is a maximum.
c. The meteor has kinetic energy and gravitational potential energy. As it approaches the earth,
its kinetic energy increases and its gravitational potential energy decreases. Just before it hits the
earth it kinetic energy is maximum and its gravitational potential energy is zero. After it hits the
earth (it is now a meteorite), what happened to its energy? Note that we have neglected it partially
burning up as it traveled through the atmosphere.
d. The apple has gravitational potential energy when hanging from the tree and no kinetic energy.
When it drops the gravitational potential energy is converted to kinetic energy.
10. Greatest gravitational potential energy: A
Greatest kinetic energy: B
11. Greatest gravitational potential energy: A
Greatest kinetic energy: C
12. When falling at its terminal velocity, the rock’s kinetic energy remains constant, but its gravitational
potential energy becomes less. This lose in gravitational potential energy is being converted into
heat.