====== Five Steps ====== According to Physics legend Mr. Brian Fudacz, Physics is __not__ math class and should be treated with high intellectual esteem. I don't really give a fuck but if we don't do these five steps we get points docked off on tests. ===== Steps ===== - Draw a picture of the scenario - Identify all variables needed for the [[physics:kinematic_equations|Kinematic Equations]] - Choose and write down the __unmodified__ equation variation - Plug and chug for a solution - Verify that the solution is valid and sensible for the scenario ===== Example ===== > A model rocket is launched straight upward with an initial speed of **50.0 m/s**. It accelerates with a constant upward acceleration of **2.00 m/s^2** until its engines stop at an altitude of **150 m**. - What is the maximum height reached by the rocket? - How long after lift-off does the rocket reach its maximum height? - How long is the rocket in the air? ==== Step 1 ==== FIXME Draw shitty pictures in GIMP === Part 1 === Part 1 represents when the rocket is being launched into the air. === Part 2 === Part 2 represents when the rocket is slowing to its top of decent. === Part 3 === Part 3 represents the rocket falling back to earth. ==== Step 2 ==== === Variables === == Part 1 == * $V_i = 50.0 \text{ m/s}$ * $a = 2.00 \text{ m/s^2}$ * $D = 150 \text{ m}$ * $V_f = \text{ ?}$ * $t = \text{ ?}$ == Part 2 == * $V_i = V_f$((part 1's answer)) * $V_f = 0$ * $a = -9.8 \text{ m/s^2}$((gravity)) * $D = \text{ ?}$ * $t = \text{ ?}$ == Part 3 == * $D = 150 + D$((part 2's answer)) * $a = -9.8 \text{ m/s^2}$ * $V_i = 0$ * $t = \text{ ?}$ === Answers === - $= D_1 + D_2$ - $= t_2$ - $= t_1 + t_2$ ==== Step 3 ==== === Equations === - $V_f^2 = V_i^2 + 2aD$ - $V_f = V_i + at$ - $V_f^2 = V_i^2 + 2aD$ (Part 2) - $V_f = V_i + at$ (Part 2) - $D = V_it + \frac{1}{2}at^2$ (Part 3) ==== Step 4 ==== === Equation 1 === - $V_f^2 = (50.0)^2 + 2(2.00)(150)$ - $V_f^2 = 2500 + 600$ - $V_f^2 = 3100$ - $\sqrt{V_f^2} = \pm\sqrt{3100}$ - $\boxed{V_f = 55.6 \text{ m/s}}$((negative is discarded as it doesn't make sense in context)) === Equation 2 === - $55.6 = 50.0 + 2.00t$ - $5.6 = 2t$ - $\boxed{t = 2.8 \text{ secs}}$ === Equation 3 === - $0 = (55.6)^2 + 2(-9.8)D$ - $0 = 3091.36 + -19.6D$ - $-3091.36 = -19.6D$ - $\boxed{D = 157.7 \text{ m}}$ === Equation 4 === - $0 = 55.6 + -9.8t$ - $-55.6 = -9.8t$ - $\boxed{t = 5.7 \text{ secs}}$ === Equation 5 === - $307.7 = 0t + \frac{1}{2}(9.8)t^2$((gravity isn't negative here; in the context of the problem, negative time wouldn't make sense)) - $307.7 = 4.9t$ - $\boxed{t = 7.9 \text { secs}}$ ==== Step 5 ==== - $\boxed{307.7 \text{ m}} = D$((part 3's D value)) $\checkmark$ - $\boxed{8.5 \text{ secs}} = t + t$((sum of the times of part 1 and 2)) $\checkmark$ - $\boxed{16.4 \text{ secs}} = 8.5 + t$((part 3's answer)) $\checkmark$