==2004-2005 P.O.D.s== ==RSLG== Mo-PODs (motion) 14 MAR 2005 Q. What is shown by a graph of distance vs. time? A. Speed Q. What is shown by a graph of velocity (speed) vs. time? A. Acceleration -- 17 MAR 2005 Q. Look *carefully* at the graph you created yesterday (KoT, Avg Spd vs. Dist) -- does it *really* show acceleration? A. No! Avg Spd vs. Time shows acceleration!!! -- 28 MAR 2005 mo-PODs KoT graph of velocity vs. time, showing three line segments: A; B; C. Q. Which line segment shows negative acceleration? A. "C." v(final) - v(initial) = negative number; neg. no. / pos. no. = neg. answer Q. During line segment "B," the truck's acceleration is __________. (A) positive; (B) zero; (C) changing; (D) negative A. Zero. v(final) - v(initial) = 0; 0 / anything = 0 -- 29 MAR 2005 Q. A racecar (I love palindromes!) drives around a perfectly circular racetrack at a constant speed of 55 mph. Is the racecar accelerating? A. Velocity = speed PLUS direction. Although the speed of the racecar is constant, its direction is changing constantly, therefore it *is* accelerating. [Begin Future PODs] Mo-PODs [excerpted from PC folder, Physics - Motion - Good PODs] Q. Can two objects have the same speed but different velocities? A. One object going north the other object going south, for example. Q. Can you accelerate while traveling at constant velocity? A. No. Q. Can you accelerate while traveling at constant speed? A. Yes, change direction. Example | Constant Speed? | Constant velocity? Cruise control on straight highway | yes | yes Speeding car slowing down | no | no, speed changing Going around circular track (cruise control) | yes | no, direction changing Roller coaster up-down, slowing down, speeding up | no | no, direction and speed change [End Future PODs] -- 01 APR 2005 Q. How much work is done when a 500 g mass is dragged 200 cm with a force of 5 N? A. W = F x d; W = 5N x 2m; W = 10N-m or 10J -- 13 APR 2005 Q. You may have noticed the door to the classroom has two handles: one located near the outer edge of the door; and one located near the inner edge of the door (close to the hinges). Which one of the two door handles will require less effort force in order to close the door? Explain your answer. A. The handle near the outer edge; the force-distance tradeoff explains... -- 18 APR 2005 Q. Look at the following picture of an MPV: http://www.wsanford.com/~wsanford/gr8ps/red/mpv/pulleycar-m.jpg List all of the simple machines used as part of the MPV. A. wheel & axle, lever, pulley -- 19 APR 2005 Q. If the diameter of a CD-ROM is 12 cm, then what is its circumference? A. C = pi x D, or 3.14 x 12 cm = 37.68 cm Q. In order to travel 5 m, how many times must the CD rotate? A. 500 cm / 37.68 cm = 13.27x -- 27 APR 2005 Q. Given formula F = m x a, solve for acceleration (a). What is the mathematical relationship between a & F; a & m? A. a = F/m; direct; indirect (inverse). Q. Given formula W = F x d, solve for force (F). If the work done is constant, then what is the mathematical relationship between F & d? A. F = W/d; indirect. ==2005-2006 P.O.D.s== ==RSLG== 09 MAY 2006 (Mo-PODs) Q. What is "ultrasound?" [throw-back POD] A. "Beyond" sound, that is, sound that is beyond the normal range of human hearing (20-20,000 Hz). Q. How does the motion detector use ultrasound to determine the distance to an object? A1. emit/receive. 1/2 travel time x speed of sound A2. We know the speed of sound (~343 m/s or ~750 miles/hour). Distance to target = travel time (TT), to & from target (s) * 343 m/s / 2 -- 10-11 MAY 2006 (Mo-PODs) Q. What is shown by a graph of distance vs. time? A. (Average) Speed avg speed (s) = total distance (d) / total time (t) HONORS: Q. If the speed of sound is 343 m/s, then what is the travel time to a target 3 m from the motion detector? A. 3m = TTs * 343m/s / 2 Note: "TTs" is really TT-sub-s (s= seconds, written as a subscript) 3m * 2 = TTs * 343m/s 3m * 2 / 343m/s = TTs TTs = 0.017 or 0.02 sec Per. 2,3: Q. Refer to RSLG, p. 5, Position Match 4. What is the average speed during the second line segment? A. 1 m / 3 sec = 0.333 m/sec -- 12 MAY 2006 Q. Refer to the following graph (showing acceleration): Distance-Match-2_modified_ver2.xmbl What is the _average speed_ for the 10-sec. time period shown by the graph? A. 0.2 m/sec, ~equal to mid-point of graph. *** NOTE *** For a RICH source of RSLG-related PODs, refer the following resource: http://www.wsanford.com/~wsanford/gr8ps/04_red/assessment/ RSLG_Test-Item-Bank.txt *** END NOTE *** -- 22 MAY 2006 "Gravity's Pull" Problem: Use overhead transparency master, "Newton Spring Scale" (T23) to test the spring scale "readability (metric)" in newtons. Q. What is the weight (N) of the object(s) shown on the overhead transparency? [Object A, B, C, etc.] <-- Note: In "Gravity's Pull," title of data table column = "Object" A. [answers will vary, e.g., 4.9 N] Q. What is the weight of a(n) 500-gram object? A. convert grams to kg (0.5 kg); multiply by 9.8 N (4.9 N) -- 30 MAY 2006 Q. What is shown by a graph of distance vs. time? A. Speed Q. What is shown by a graph of velocity (speed) vs. time? A. Acceleration -- 31 MAY 2006 Q. Look *carefully* at the graph you created yesterday (KoT, Avg Spd vs. Dist) -- does it *really* show acceleration? A. No! Avg Spd vs. Time shows acceleration!!! [demo 04_red/03_keep_on_truckin/KoT_Part2_v4a_analyzed.xmbl] Q. Problem(s) re: positive- & negative acceleration using formula: a = v(f) - v(i) / t A. ? -- 05 JUN 2006 P.O.D. Q. Which one of Newton's Three Laws of Motion is illustrated by the comic (shown left)? extras/bc0807g.gif A. Law 1 [inertia] -- 09 JUN 2006 Q. How much work is done to lift a 500-g mass 20 cm? (Hint: See "Work Made Easy" re: force required to lift a 500-g mass.) A. W = 5N x .2m or 1N-m or 1J Q. Given the formula for work, solve for _force_. What is the mathematical relationship between F & d? A. Given constant W, then F & d are inversely related. -- 12 JUN 2006 P.O.D.s (or "Bell WORK"): Q. What type of simple machine is a see-saw? A. Lever Q. When "playing" on a see-saw, how could a small child (on one side) lift a large adult (on the other side)? A. If the child sits on one end of the see-saw, then the adult must sit nearer the fulcrum of the lever (see-saw). [Test this idea: Hang one 500g mass on the F(e) end of the meter stick; wrap a rubber band around a meter stick and hang two 500g masses from the rubber band; move the rubber band back & forth in order to find the balance point.]