Question

1.A solid cylinder rolls without slipping down a 30° slope. Find the minimum coefficient of friction needed to prevent slipping.

2.A rectangular block 0.25m wide and 0.5m height is dragged to the right along a level surface at constant speed by a horizontal force P (acting on the right side of the block with height h above the level surface) Find the value of h at which the block just starts to tip (a) 0.4375m (b) 0.3125m (c) 0.1375m (d) 0.0375m (e) 0.15m

3.A particle is undergoing constant acceleration while the position and time are recorded.The data shows time t(s) and position x (m) in the following t(x) format :0(0),1(2),4(32). What is the distance of travel of this particle in the 4 th second?

(a) 18 m (b) 14m (c) 32m (d) 25m (e) 8m

4.A sinusoidal wave with an amplitude of 1.0cm and a frequency of 100 Hz travels at 200 m/s in the positive x-direction. At t=0s, the point x=0m is on a crest of the wave. Which one of the following functions can describe the wave mentioned above? (a) sin(πx - 200πt) (b) cos(πx- 200πt)

(c) cos(πx +200πt) (d) sin(πx-200πt+2π/3)

(e) cos(πx- 100πt)

5.A photon can be materialized into an electron and a positron. This process is called as "pair production" and cannot happen with the photon of blue light because

(a) the photon of blue light does not have enough energy.

(b) blue light can be seen by human eyes.

(c) blue light is easy to be scattered by air.

(d) blue light is not easily available.

(e) none of above.

6.Add one mole of water to a large quantity of water, the volume change is 18 cm3. Now we add one mole of water to a large quantity of ethanol, the volume change becomes 14 cm. Therefore, we know:

(a) For water-ethanol solution, water is solvent.

(b) Ethanol-water bonds are weaker than water-water bonds.

(c)Water-ethanol solution is not Raoultian.

(d)In the water-ethanol solution, the water molecules stick together.

(e) The volume change can be calculated using

ax ! T、Comp.

Answer 1

Step 1 Step 2 tau = I alpha tau = I a/R (mg cos theta mu)R = mR^2/2 times a/R a = 2g cos theta mu Step 3 sigma F_x = ma mg sin theta - mu mg cos theta = ma g sin theta - mu g cos theta = a Put = > a = 2 g cos theta mu g sin theta - mu g cos theta = 2g cos theta mu sin theta = 3 cos theta mu mu = 1/3 tan theta = 1/3 tan 30 degree = 0.1924

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