PL-3) Jane uses a stopwatch to measure the time the apparatus takes to complete

Question

PL-3) Jane uses a stopwatch to measure the time the apparatus takes to complete three full revolutions (she starts and stops the watch as the bob passes the pointer); she measures the time to be 4.2 s. What is the period of rotation in seconds?

PL-4) In a separate trial, Jane determines the period to be 2.14 sec. With the apparatus stopped, she measures the radius to be 13.2 cm and the mass of the bob (B) to be 253 g. What was the centripetal force on the bob, in newtons, while it was in uniform circular motion?

Explanation / Answer

PL-3)     period of rotation in seconds =   4.2/3   =   1.4 sec

PL-4)      centripetal force on the bob   = m * w2 * r

                                                             =   0.253 * (2 * 3.14/2.14)2 * 0.132

                                                              =   0.287 N

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