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Solving Physics Problems

Solving Physics Problems. Problem Solving Strategy. Read the Question. Make a sketch. Take Inventory. Identify principles. Select a formula. Isolate variables. Substitute and Solve. Check Your Answer. 1. Read the question.

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Solving Physics Problems

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  1. Solving Physics Problems

  2. Problem Solving Strategy Read the Question Make a sketch Take Inventory Identify principles Select a formula Isolate variables Substitute and Solve Check Your Answer

  3. 1. Read the question • Seriously, before you start your journey, you need to know where you are going. Understand the question before proceeding! • Identify the exact variable you are being asked to find (using standard notation) • V0 (initial velocity)? • FNET (net force)?

  4. 2. Make a sketch • Ancient proverb: one picture is worth a thousand words • Select a coordinate system and establish positive directions (up and right are often positive) • Remember, do not assume your sketch is accurate: do not make measurements on your sketch

  5. 3. Take an inventory • Extract variables from the problem • Identify or make assumptions about initial conditions • Document this data in the appropriate places on your sketch • Record all data with associated units • Learn and use standard symbols: a for acceleration, v for velocity, etc.

  6. 4. Identify Physical Principles • Problems assigned to you are meant to reinforce learning lessons – what physical principles apply: • Is object in equilibrium? • Is system open or closed? • Are conservation laws applicable? • Divide and conquer • Are different principles dominant at different time intervals during the problem?

  7. 5. Select a formula • Based on unknown and known data, identify a given equation that shows promise • Write this equation in algebraic form before proceeding • Make sure you know (n-1) of the (n) variables in the formula

  8. 6. Isolate the variable • Algebraically manipulate your chosen equation to isolate the unknown variable on one side • Check again to make sure the variables on the other side of the equation are all known values (given or assumed) • Simplify the algebra, if possible

  9. 7. Substitute and solve • Insert all known values into your chosen equation • Include units with all values • Remember algebra applies to units as well as numbers • Look for unit cancellations • (for example: m/s2 x s = m/s)

  10. 8. Check your results • Did the units match the expected answer? • Can you estimate expected answer (i.e. order of magnitude)? • Can you predict minimum or maximum values for the expected answer? • Should answer be bigger or smaller than data provided in problem?

  11. Subscripts • v = v0 + at • d = d0 + v0t + ½at2 • Values with subscripts denote specific values, usually at specific times • x 0 or x i for initial conditions, x f for final • Values without a subscript are usually variables, sometimes constants

  12. Delta Notation • Δx = xfinal – xinitial (xf – xi) • Alternate: Δx = x1 – x0 (some books might use x2 – x1) • x0 → x “naught” (typically, this is the initial condition) • Can you assume initial condition = zero? • In that case, Δx = x • Units of Δx are the same as x

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