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A big THANK YOU to major league baseball for finally enforcing a pitch clock. I've watched more games already this year than in the last four years combined. It's not a complicated game. Pick a pitch and throw it. If you give up a home run, another 20 seconds of thought would not have changed that.
Similarly, don't take more than five minutes for one of these fundamentals checks! This is recall, not problem solving. If you don't know the answer, more time isn't going to change that. Just do your best, and learn from what you get wrong.
FUNDAMENTALS CHECK #5
41. Under what conditions are the kinematics equations valid?
42. How do you determine instantaneous speed from a curved position-time graph?
43. Which way is the object moving?
44. Is the object speeding up or slowing down?
45. What is the direction of the object's acceleration?
46. Write the standard kinematics equation for displacement.
47. An object moves in a circle. What is the magnitude and direction of the object's acceleration?
48. Cart A moves east with momentum 30 Ns; cart B moves north with momentum 40 Ns. What is the magnitude of the momentum of the two-cart system?
49. Write the equation relating torque to angular momentum.
50. What is determined from the area under a force vs. time graph?
Solutions to fundamentals check 5:
ReplyDelete41. when an object has constant acceleration.
42. by taking the slope of a tangent line to the curve.
43. left. (The v-t graph is below the horizontal axis, which means motion in the negative direction, which is left.)
44. slowing down. (The vertical axis of the v-t graph is speed - the vertical axis values get closer to zero, so the speed gets closer to zero.)
45. right. (When an object slows down, acceleration is opposite the direction of motion. Motion is left, slowing down, so acceleration is right.)
46. displacement = v0t + (1/2)at^2.
47. magnitude is v^2/r; direction is toward the circle's center.
48. 50 Ns. (Momentum is a vector, so add the perpendicular components using pythagoras.)
49. Change in angular momentum equals (net)torque times time. (Usually written as delta-L = tau*t.)
50. impulse.
Not to quibble but I think #47 is in error. The answer as given is certainly the /centripetal/ part of the acceleration, but if the object is accelerating around the circle, there would be a /tangential/ component as well. In that case, the actual acceleration would point along the vector sum of these two and thus not be radially inward (and would have a magnitude greater than v^2/r to boot).
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