F.4 physics

xtina

2010-04-20 7:18 am

a bob of mass 10g is connected to a vertical pole by two identical light strings of length 1m. it is then set into uniform circular motion with a period of 1.5s, and the strings make an angle of 45^o with the pole as shown.
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a)do you think the tensions in the strings are equal?why?
b)calculate the tensions in the strings.

回答 (1)

Prof. Physics

2010-04-20 4:37 pm

✔ 最佳答案

a. The tensions in the strings are not equal, since the vertical component of the upper tension has to balance the vertical component of the lower tension and the weight of the bob.

b. Let T, T' be the tensions in the upper string and the lower string respectively.

Tsin45* + T'sin45* = m(lsin45*)w^2

T + T' = (0.01)(1)(2pi/1.5)^2

T + T' = 0.175 ... (1)

Tcos45* = T'cos45* + mg

T/sqrt2 = T'/sqrt2 + (0.01)(10)

T - T' = 0.141 ... (2)

Solving (1) and (2),

T = 0.158 N, T' = 0.017 N

參考: Physics king

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