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Journal Entry #5 = work for Friction WA #s 4 and 5 Warm-up: 12/14/15 (#6) Jane and John, with masses of 50 kg and 60 kg, respectively, stand on a frictionless surface 10 m apart. John pulls on a rope that connects him to Jane, giving Jane an acceleration of 0.92 m/s2 toward him. (a) What is John's acceleration? (b) If the pulling force is applied constantly, how far from John's starting position will they meet? Warm-up: 12.15.15 (#7) A large (75.0 kg) crate first starts sliding down a ramp when the ramp makes an angle of 37° with the horizontal. a) Draw a free-body diagram for the crate b) What is the coefficient of static friction between the crate and the ramp? c) What is the acceleration of the crate if the angle is not changed? (coefficient of dynamic friction is 0.55) d) If the coefficient of dynamic friction is 0.55, what angle will allow the box to slide at a constant velocity? Warm-up 12.16.15 (#8) The coefficients of static and kinetic friction between a 33 kg box and a horizontal surface are 0.74 and 0.17, respectively. (a) What is the acceleration of the object if a 345 N horizontal force is applied to the box? (b) What is the acceleration if the applied force is 450 N Warm-up: 1.4.16 (#9) Remind yourself of all the topics we have been covering in this class in the past several weeks (i.e. since Thanksgiving-ish) Warm-up: 1.5.16 (#10) A cabinet door is open, and you don’t want to stand up to close it. You do, however, have a tennis ball and a ball of clay near you. You choose to throw one of them at the door (they have the same mass). The tennis ball will bounce off the door (but not back to you), and the clay will stick to it before falling off. Which would you choose as being the most likely to close the door? Why? Warm-up #11 is in the Momentum/Impulse Notes Warm-up #12 is the Frog Physics lab Warm-up #13 is in the Momentum/Impulse notes (What is momentum?) Warm-up #14: How did you collect frog lab data? What is the momentum of the frog? Would the impulse felt by the frog be affected by a stronger spring? How would this impact the momentum change of the frog? Warm-up #15: (1/8/16) Video notes on the Modern Marvels Crashes video (green worksheet)—excused from this one if you were at DECA and/or had an excused absence. Warm-up #16: 1/11/16 A 13.0 g bullet, traveling at 235 m/s, penetrates a wall and emerges with a velocity of 175 m/s. - What force has been exerted by the wall on the bullet if it passed through the wall in 25.0 ms? - What Impulse will stop the bullet after it leaves the wall? Warm-up 1.12.16 (#17) Define Impulse If a 1250 kg car traveling at 15.5 m·s-1 is stopped in 0.750 s, what stopping force must have been applied? Sketch a Force-Time graph illustrating the stopping of the car Warm-up: 1/13/16 (#18) During a crash test, a 1250 kg car traveling at 25.5 m·s-1 hits a wall and comes to a stop in 0.0763 s. What is the average net force acting on the car to bring it to a stop? Assume the second crash test (involving the same type of car) has the car initially traveling at 18.0 m·s-1, but the car experiences the same average net force through a time of 0.0675 s. What is the final velocity of this car?