Physics 2010 Sid Rudolph General Physics Mathematics Review These documents in mathematics are intended as a brief review of operations and methods. Early in this course, you should be totally familiar with basic algebraic techniques, some analytic geometry, and trigonometry. SCIENTIFIC NOTATION Many quantities that scientists deal with often have very large or very small values. For example, the speed of light is about 300 000 000 m/s and the ink required to make the dot over an i in this document has a mass of about 0.000 000 001 kg. Obviously, it is very cumbersome to read, write, and keep track of numbers such as these. We avoid this problem by using a method dealing with powers of the number 10: 10 10 1 = 10 10 2 = 10 x 10 = 100 10 3 = 10 x 10 x 10 = 1000 10 4 = 10 x 10 x 10 x 10 = 10 000 10 5 = 10 x 10 x 10 x 10 x 10 = 100 000 and so on. The number of zeros corresponds to the power to which 10 is raised called the exponent of 10. For example, the speed of light, 300 000 000 m/s, can be expressed as 3 x 10 8 m/s. For numbers less than one, we note the following: 10-1 = 1/10 = 0.1 10-2 = 1/100 = 1/(10 x 10) = 0.01 10-3 = 1/1000 = 1/(10 x 10 x 10) = 0.001 10-4 = 1/10 000 = 1/(10 x 10 x 10 x 10) = 0.0001 10-5 = 1/100 000 = 1/(10 x 10 x 10 x 10 x 10) = 0.00001 In these cases, the number of places the decimal point is to the left of the digit 1 equals the value of the (negative) exponent. Numbers that are expressed as some power of 10 multiplied by another number between 1 and 10 are said to be in scientific notation. For example, the scientific notation for 5 943 000 000 is 5.943 X 10 9 and that for 0.0000832 is 8.32 x 10-5. When numbers expressed in scientific notation are being multiplied, the following general rule is very useful:
10 n x 10 m = 10 n+m where n and m can be any numbers (not necessarily integers). For example, 10 2 x 10 5 = 10 7. The rule also applies if one of the exponents is negative. For example, 10 3 x 10-8 = 10-5. When dividing numbers expressed in scientific notation, note that 10 n /10 m = 10 n x 10 -m = 10 n-m With help from the above rules, complete the following and/or express in scientific notation: 1. 86,400 = 2. 9,816,762.5 = 3. 0.0000000398 = 4. (4 x 10 8 )(9 x 10 9 ) = 5. (3 x 10 7 )(6 x 10-12 ) = 6. 75 x 10-11 /5 x 10-3 = 7. (3 x 10 6 )(8 x 10-2 )/(2 x 10 17 )(6 x 10 5 ) = Note: the two numbers to the right of the divide ( / ) symbol are in the denominator. ALGEBRA Some Basic Rules: When algebraic operations are performed, the laws of arithmetic apply. Symbols such as x, y, and z are usually used to represent quantities that are not specified, what are called the unknowns. First, consider the equation 8x = 32 If we wish to solve for x, we can divide (or multiply) each side of the equation by the same factor without destroying the equality. In this case, if we divide both sides by 8, we have Next consider the equation 8x/8 = 32/8 x = 4 x + 2 = 8 In this type of expression, we can add or subtract the same quantity from each side. If we subtract 2 from each side, we get
x + 2-2 = 8-2 x=6 In general, if x + a = b, then x = b - a. Now consider the equation x/5 = 9 If we multiply each side by 5, we are left with x on the left by itself and 45 on the right: (x/5) (5) = 9 x 5 x = 45 In all cases, whatever operation is performed on the left side of the equality must also be performed on the right side. The following rules for multiplying, dividing, adding, and subtracting fractions should be recalled, where a, b, and c are three numbers: Rule Example Multiplying (a/b)(c/d) = ac (2/3)(4/5) = 8/15 bd Dividing (a/b) = ad 2/3 = 10 (c/d) cb 4/5 12 Adding a/b ± c/d = ad+bc 2/3-4/5 = bd (2)(5) - (4)(3) (3)(5) = -(2/15) In the following exercises, solve for x: 4. a = 1/(1+x) 5. 3x - 5 = 13
6. ax - 5 = bx + 2 7. 5/(2x + 6) = 3/(4x + 8) Powers When powers of a given quantity x are multiplied, the following rule applies: x n x m = x n+m For example, x 2 x 4 = x 2+4 = x 6. When dividing the powers of a given quantity, the rule is For example, x 8 /x 2 = x 8-2 = x 6. x n /x m = x n-m A power that is a fraction, such as 1/3, corresponds to a root as follows: TABLE Rules of Exponents x 0 = 1 x 1 = x x n x m = x n+m x n /x m = x n-m x 1/n = n x (x n ) m = x nm x 1/n = n x (the nth root of x) For example, 4 1/3 = 3 4 = 1.5874. (A scientific calculator is useful for such calculations.) Finally, any quantity x n that is raised to the m th power is(x n ) rn = x nrn The table above summarizes the rules of exponents. Complete the following: 1. 3 2 x 3 3 =
2. x 5 x -8 = 3. x 10 /x -5 = 4. 5 1/3 = (Use your calculator.) 5. 60 1/4 = (Use your calculator.) 6. (x 4 ) 3 = Factoring Some useful formulas for factoring an equation are ax + ay + az = a(x + y + x) a 2 + 2ab + b 2 = (a + h) 2 a 2 - b 2 = (a + b)(a - b) common factor perfect square differences of squares Quadratic Equations The general form of a quadratic equation is ax 2 + bx + c = 0 where x is the unknown quantity and a, b, and c are numerical factors referred to as coefficients of the equation. This equation has two roots, given by b b ac x = ± 2 + 4 2a EXAMPLE 1 The equation x 2 + 5x + 4 = 0 has the following roots corresponding to the two signs of the square-root term: x = 5± 5 2 ( 4 )( 1 )( 4 ) = 5 ± 9 = 5 ± 3 2( 1) 2 2
x + = 5 + 3 = 1 x 2 = 5 3 = 4 2 where x + refers to the root corresponding to the positive sign and x - refers to the root corresponding to the negative sign. Solve the following quadratic equations: 1. x 2 + 2x -3 =0 2. 2x 2-5x +2 = 0 3. 2x 2-4x -9 = 0 Linear Equations A linear equation has the general form y = ax + b where a and b are constants. This equation is referred to as being linear because the graph of y versus x is a straight line, as shown in figures below. The constant b, called the intercept, represents the value of y at which the straight line intersects they axis. The constant a is equal to the slope of the straight line and is also equal to the tangent of the angle that the line makes with the x axis. If any two points on the straight line are specified by the coordinates (x 1, y 1 ) and (x 2, y 2 ), as in figure, then the slope of the straight line can be expressed as Slope = y x y x 2 1 2 1 y = = tanθ x
Note that a and b can have either positive or negative values. If a> 0, the straight line has a positive slope, as in figures. If a < 0, the straight line has a negative slope. In figure to the left above, both a and b are positive. Three other possible situations are shown in right figure above: a> 0, b < 0; a < 0, b> 0;and a < 0, b <0. 1. Draw graphs of the following straight lines: (a) y = 5x + 3 (b) y = -2x + 4 (c) y = -3x - 6 2. Find the slopes of the straight lines described in Exercise 1.3 3. Find the slopes of the straight lines that pass through the following sets of points. (a) (0, -4) and (4, 2) (b) (0, 0) and (2,-5), and (c) (-5, 2) and (4, -2) Solving Simultaneous Linear Equations Consider an equation such as 3x + 5y = 15, which has two unknowns, x and y. Such an equation does not have a unique solution. That is, (x = 0, y = 3), (x = 5, y = 0), and (x = 2, y = 9/5) are all solutions to this equation. If a problem has two unknowns, a unique solution is possible only if we have two equations. In general, if a problem has n unknowns, its solution requires n independent equations. In order to solve two simultaneous equations involving two unknowns, x and y, we solve one of the equations for x in terms of y and substitute this expression into the other equation. EXAMPLE 2 Solve the following two simultaneous equations: (1) 5x + y = -8 (2)2x - 2y = 4
Solution From (2), x = y + 2 (How was this obtained from (2)?), substitution of this into (1) gives 5(y + 2) + y = -8 6y = -18 y = -3 x = y + 2 = -1 Alternate Solution Multiply each term in (1) by the factor 2 and add the result to (2): l0x + 2y= -16 2x - 2y = 4 12x + 0y = -12 x = -1 y = x - 2 = -3 (It is not necessary to put in the 0y. It is included to show how the y terms cancel.) Two linear equations with two unknowns can also be solved by a graphical method. If the straight lines corresponding to the two equations are plotted in a conventional coordinate system, the intersection of the two lines represents the solution. For example, consider the two equations x - y = 2 x - 2y = -1 These are plotted in figure below. The intersection of the two lines has the coordinates x = 5, y =3. This represents the solution to the equations. You should check this solution by the analytical technique discussed above.
Solve the following pairs of simultaneous equations involving two unknowns: 1. x + y = 8 x - y =2 2. 98 - T = l0a T - 49 = 5a 3. 6r + 2y = 6 8r - 4y = 28