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# Lect05 - m1 m2 m3 m4 m5 Physics 211 Lecture 5 Today's...

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Unformatted text preview: m1 m2 m3 m4 m5 Physics 211 Lecture 5 Today's Concepts: a) Free Body Diagrams Free b) Force due to strings Force c) Force due to springs Force d) Force due to gravity Force Physics 211 Lecture 5, Slide 1 Physics Stuff you asked about: Nothing was particularly confusing. You guys rock. The part with the moon and how it proved the universal law of gravitation. How to find equations for tension and normal force when an object is on an angled surface Calculating the acceleration the moon experienced from the earth confused me. Did the calculation mean that the moon experiences the same acceleration as the apple? How can that be if the moon is so much farther away from the earth than an apple on the surface? Can we go over it in class??? Elevator scenarios Springs. Also, U of I got DESTROYED by Missouri despite all of the professor's trash talking. Physics 211 Lecture 5, Slide 2 Physics Act You are traveling on an elevator up the Sears tower. As you near the top floor, your weight appears to be A) Heavier B) Lighter C) Unchanged Physics 211 Lecture 5, Slide 3 Physics Preflight A box of mass m is hung with a string from the ceiling of an elevator that is accelerating upward. Which of the following best describes the tension T in the string: A) T = mg B) T > mg C) T < mg Since it is accelerating upward, Ft is equal to mg + ma, so it is great than that weight of the box, which is just mg. a m Physics 211 Lecture 5, Slide 4 Physics Preflight A box of mass m is hung by a spring is from the ceiling of an elevator. When the elevator is at rest the length of the spring is L = 1m. If the 1m elevator accelerates upward the length of the spring will be A) L = 1 m B) L < 1 m C) L > 1 m For the same reason the string has more tension, the spring will stretch more. Physics 211 Lecture 5, Slide 5 Physics L m a Act This is an explanation from someone who got the last question right: “The fact that the elevator is accelerating upward will produce more downward force on the box. This will stretch the spring more than usual, making the length greater than when the spring is at rest.” Do you agree: A) YES B) NO Physics 211 Lecture 5, Slide 6 Physics Physics 211 Lecture 5, Slide 7 Physics Physics 211 Lecture 5, Slide 8 Physics Physics 211 Lecture 5, Slide 9 Physics Preflight A block sits at rest on a horizontal frictionless surface. Which of the following sketches most closely resembles the correct free body diagram for all forces acting on the block? Each red arrow represents a force. A B C D The only forces acting on the box are gravity (acting downward) and normal force (acting upward). Physics 211 Lecture 5, Slide 10 Physics Act A block slides down a frictionless inclined plane. Which of the following sketches most closely resembles the correct free body diagram for all forces acting on the block? Each red arrow represents a force. A B C D Physics 211 Lecture 5, Slide 11 Physics Act A cart with mass m2 is connected to a mass m1 using a is using string that passes over a frictionless pulley, as shown below. The cart is held motionless. m2 The tension in the string is A) B) C) m1 g m1g m2g 0 Physics 211 Lecture 5, Slide 12 Physics Act A cart with mass m2 is connected to a mass m1 using a is using string that passes over a frictionless pulley, as shown below. Initially, the cart is held motionless, but is then released and starts to accelerate. a m2 After the cart is released, the tension in the string is A) = m1g B) > m1g C) < m1g m1 g Physics 211 Lecture 5, Slide 13 Physics A pair of forces is missing !! Physics 211 Lecture 5, Slide 14 Physics Physics 211 Lecture 5, Slide 15 Physics Act An astronaut on Earth kicks a bowling ball straight An ahead and hurts his foot. A year later, the same astronaut kicks a bowling ball on the moon in the same manner with the same force. His foot hurts... A) B) B) C) C) more more less less the same the The masses of both the bowling ball and the The masses astronaut remain the same, so his foot will feel the same resistance and hurt the same as before. same Ouch. Act A block weighing 4 lbs is hung from a rope attached to a scale. The scale is then attached to a wall and reads 4 lbs. What will the scale read when it is instead attached to another block weighing 4 lbs? ? m m m A) 0 lbs. lbs. B) 4 lbs. B) lbs. C) C) 8 lbs. lbs. ...
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