题目内容

A spherical transparent body, whose refractive index is (), can focus a near-axis parallel beam from infinity on the vertex of the second plane.

A. 1.5
B. 2

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When a train leaves the station at a speed of 66m/s and whistles at a frequency of 1800Hz, set the sound velocity in the air is 330m/s and the sound frequency you will hear at the station will be ().

A. 2200 Hz
B. 1500Hz
C. 2400 Hz
D. 2000 Hz

For a steady flow in the pipe, at one place the cross-sectional area is 0.5 ㎝2 and the speed is 12 ㎝/ s, then at another place where the speed is 4 ㎝/ s, the cross-sectional area is: ()

A. 1.0㎝2
B. 1.5㎝2
C. 2.0㎝2
D. 2.15㎝2

When using stokes law to measure the viscosity of a fluid, the object used should be :()

A. small cylindrical object
B. large cylindrical object
C. small spherical object
D. large spherical object

If the diameter of a certain blood vessel is doubled, and all else remains unchanged, the blood flow through it becomes () the original value.

A. 2 times
B. 1/2 times
C. 4 times
D. 16 times