F6 Phy - Ans.fyi 參考答案

F6 Phy

[匿名]

2009-07-17 9:45 am

1Two forces p and q have a resultant force r

with a max. value of 60 N and a minimum value of 10N

Find r if the angle (feta) between p and q is 40 degree.

2 reading of voltmetre 1.30+-0.01V

----------------ammeter 0.76+-0.01A

length of the wire 75.4+-0.2cm

diameter of the wire 0.54+-0.02 mm

Cal. with the actual uncertainty, the value of

a the resistance of the wire.
b the resistivity of the metal of wire .

If you have the Qs ,Please answer 3
3 2002 HKALE iiA Q45 MC (Phy)

回答 (1)

Prof. Physics

2009-07-17 3:22 pm

✔ 最佳答案

1. Max: p + q = 60 ... (1)

Min: p - q = 10 ... (2)

Solving (1) and (2), p = 35 N, q = 25 N

By cosine law,

r = sqrt[p2 + q2 - 2pqcos(180* - 40*)]

= sqrt[(35)2 + (25)2 - 2(35)(25)cos140*]

= 56.5 N

2. Resistance, R = V / I = 1.30 / 0.76 = 1.71 ohms

│@R / R│ = │@V / V│+│@I / I│

@R / 1.71 = 0.01 / 1.30 + 0.01 / 0.76

@R = 0.04 ohms

So, resistance = 1.71 +- 0.04 ohms

b. By R = pl / A = pl /pi(d/2)2

p = pi(d/2)2R / l

p = pi(0.54 X 10-3/2)2(1.71) / 0.754

Resistivity, p = 5.19 X 10-7 ohmm

│@p / p│ = 2│@d / d│+│@R/R│+│@l / l│

@p / 5.19 X 10-7 = 2(0.02/0.54) + (0.04/1.71) + (0.2/75.4)

@p = 5 X 10-8 ohmm

Resistivity = 5.2 X 10-7 +- 0.5 X 10-7 ohmm

2002. by Mass = density X volume

m = p(pi(d/2)2l)

d = 2sqrt(m/plpi)

@d / d = @m / m + @l / l

@d / d = 4% + 2%

@d / d = 6%

參考: Physics king

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