physics mock mc


1 Answer

  • 天同
    Lv 7
    7 years ago
    Favorite Answer

    1. Apply the equation: s = ut + (1/2)at^2 to the vertical motion from R to S

    with s = -10m, u = 0 m/s, a = -g(=-9.81 m/s^2), t =?

    hence, -10 = (1/2).(-9.81)t^2

    t = 1.428 s

    Hence, horizontal speed of monkey = 7/1.428 m/s = 4.9 m/s

    The answer is option B

    2. Let b be the angular position of the 4th order maximium, and c be the angular position of the 2nd order maximium.

    Hence, a.sin(c) = 2入

    and a.sin(b) = 4入

    where a is the grating slit separation and 入 is the wavelength of light used.

    Dividing, sin(c)/sin(b) = 2入/ 4入 = 1/2

    i.e. sin(c) = sin(b)/2

    The max vlaue of sin(b) = 1, hence, sin(c) < 1/2

    i.e. c < 30 degrees

    The answer is thus option B (i.e. choose the nearest angle below 30 degrees)

    [ Option A is wrong because when the 2nd order max is at 15 degrees, the max order of fringe is 7, not 4]

    3. Suppose the electron is at distance d from the -ve plate

    Change in potential of electron = (Vo).(d/D)

    where Vo is the voltage between the two plates, with separation D.

    Hence, drop in potential energy of electron = e.(Vo)(d/D)

    where e is the electronic charge

    By conservation of energy,

    (KEo) + e(Vo)(d/D) = KE

    where (KEo) is the initial kinetic energy, and KE is the kinetic energy at distance d.

    Thus, KE = [e(Vo)/D].d + (KEo)

    The graph of KE against d is a straight line with +ve slope of value [e(Vo)/D].

    The answer is option A

    4. The answer is option C.

    Statement 1 is wrong because the straight line of M doesn't pass through the origin. Hence, V and I are NOT proportional.

    5. When S is closed,

    99 = 100R/(100+R)

    R = 9900 ohms

    When S is open, the 100-ohm is in parallel with 2R

    Equivalent resistance = 100 x 2R/(100+2R) = 99.5 ohms

    The answer is option C

    (Since the "word limit" is reached, I give answer to Q6 and 7 in the opinion (意見) section.)

    2013-03-09 17:50:32 補充:

    6. Magnetic force at X due to Y and Z, Fx = [-k(2).(1)/(2) + k(2).(3)/4] = 0.5k

    where k is a constant

    Magnetic force at Y due to X and Z, Fy = [k.(1).(2)/2 k(1).(3)/2] N = 2.5k

    Magnetic force at Z due to X and Y, Fz = [k(2).(3)/4 + k(1).(3)/2] = 3k

    2013-03-09 17:51:09 補充:

    6(cont'd) Hence, the greatest magnetic force is experienced by Z, and the least force by X.

    The answer is option C.

    2013-03-09 17:51:36 補充:

    7. There are 3 forces acting on the kite, the kite weight of 0.2g, the string tension 15 N and the wind force F. The 3 forces are in equilibrium, and hence forms a triangle (Principle of Triangle of Forces). The angle bewteen the kite weight and the string tension is (90+35) degrees = 125 degrees.

    2013-03-09 17:52:03 補充:

    7(cont'd) By the cosine rule,

    F^2 = [(0.2g)^2 + 15^2 - 2 x 0.2g x 15.cos(125) ] N^2

    where g is the acceleration due to gravity

    F = 16.2 N

    The answer is option B

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