Pathways to Astronomy

Stephen E. Schneider

Chapter 20 Conservation Laws - all with Video Answers

Educators

Chapter Questions

Problem 1

A basketball has a mass of about $0.5 \mathrm{kg}$. How fast would it have to be thrown to have 1 joule of kinetic energy? Convert your answer to kph (or mph if that is more familiar to you). Is that a hard throw or a light throw?

Tara Appleyard

Numerade Educator

02:16

Problem 2

An object with a mass of $1.00 \times 10^{5} \mathrm{kg}$ is at a height of $3.00 \times 10^{6} \mathrm{m},$ headed directly away from the Earth. What energy will this object have when it comes back and strikes the Earth?

Paul Gabriel

Numerade Educator

04:04

Problem 3

Show that if the gravitational potential energy and kinetic energy add up to zero for an object on the Earth's surface, you can derive the escape velocity formula given in Unit 18.

Mir Afzal

Numerade Educator

02:32

Problem 4

Suppose that a comet with a mass of $10^{9} \mathrm{kg}$ strikes the Earth at a velocity of $40 \mathrm{km} / \mathrm{sec} .$ How much energy would be released by the impact? Convert this energy into the equivalent of "kilotons of TNT" (kt), where 1 kt $=4.2 \times 10^{12}$ joules.

Kevin Shryock

Numerade Educator

01:44

Problem 5

Astronomers estimate that about 100 metric tons $\left(1 \times 10^{5} \mathrm{kg}\right)$ of meteorites strike the Earth every day.
a. If the meteorites increased the mass of the Earth by $1 \%$ without adding any angular momentum, how long would the day become?
b. The Earth's mass is $5.97 \times 10^{24}$ kg. How many years would it take to increase the Earth's mass by $1 \%$ at this rate?

Manish Jain

Numerade Educator

07:30

Problem 6

Suppose that a star collapses inward until it is reduced to onetenth of its original size while losing no mass.
a. How many times faster will its surface be moving?
b. If initially it was spinning around once every 100 hours, how long will it take to spin around after it collapses?

Averell Hause

Carnegie Mellon University