Accel. (m/s 2 ) Time (sec) Newton s 3 rd Law and Circular Motion. Group Problem 04

Transcription

1 1) A 200 kg tuck acceleates eastwads on a hoizontal oad in esponse to a gadually inceasing fictional foce fom the gound. Thee is an unsecued 50 kg block sitting on the tuck bed line. Thee is fiction between the block and the bed line. An acceleomete is mounted in the tuck. The block acceleates with the tuck until the acceleation eaches 10 m/s 2. At that instant the block begins to slide and the tuck s acceleomete now epots a value of 11 m/s 2. What ae the coefficients of static and kinetic fiction? Accel. (m/s 2 ) 0 Time (sec)

2 1B) A 200 kg tuck can acceleate at 1.5 m/s 2. Thee is an unsecued 50 kg block sitting on the tuck bed line. Thee is fiction between the block and the bed line with static and kinetic coefficients of fiction 0.50 and 0.40 espectively. The tuck is descending on an incline which gadually gets steepe. At what angle fom hoizontal does the fiction foce go zeo? If the angle inceases to 36.9, then will the box slide (a vey steep 60% gade!)? Fo expets at home: At what angle fom hoizontal does the box just begin to slide?

3 2) A pendulum swings fom its tunaound point on the left (point 1) to its tunaound point on the ight. At each of the points: On the left hand side figue sketch the adial acceleation vecto(s) and on the ight hand side figue sketch the tangential acceleation vecto(s). 3) A toy ca with mass m 15.0g olls without fiction along a tack that goes ove a hill. The hill is in the shape of an ac of adius R 35.0cm. The foce of gavity acts on the ca at the point maked with an x. At the instant shown in the dawing its speed is m/s in the diection shown. Daw an accuate fee-body-diagam of the toy ca in the box and find all of the following vecto quantities indicated (both magnitude and diection). Clealy specify diection with espect to any unambiguous axis diection and make clea you choice of coodinate system. Show you wok. CM location v Fnet ( di.) 0.800m/s a( di.) 30º adius, R 35.0cm a. F net

4 b. a c. N T. C (Nomal foce by the tack on the ca.) d. F centipetal e. F tangential f. a centipetal g. a tangential Is thee a speed at which the nomal foce goes to zeo? If so, what is it. What do you think happens next?

5 4) A neighbo's child wants to go to a neighbohood canival to expeience the wild ides. The neighbo is woied about safety because one of the ides looks dangeous. She knows that you have taken physics and so asks you advice. The ide in question has a 10-lb chai which hangs feely fom a 30-ft long chain attached to a pivot on the top of a tall towe. When a child entes the ide, the chain is hanging staight down. The child is then attached to the chai with a seat belt and shoulde haness. When the ide stats up the chain otates about the towe. Soon the chain eaches its maximum speed and emains otating at that speed. It otates about the towe once evey 3.0 seconds. When you ask the opeato, he says that the ide is pefectly safe. He demonstates this by sitting in the stationay chai. The chain ceaks but holds and he weighs 200 lbs. Has the opeato shown that this ide safe fo a 50-lb child?