A truck moving at 36 m/s passes a police car moving at 45 m/s in the opposite direction. If the frequency of the siren relative to the police car is 500 Hz, what is the frequency heard by an observer in the truck as the police car approaches the truck? (The speed of sound in air is 343 m/s.)
a. 396
b. 636
c. 361
d. 393
e. 617
B
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Pressure in a Liquid: A container has a vertical tube, whose inner radius is 12.00 mm, connected to it at its side, as shown in the figure. An unknown liquid reaches level A in the container and level B in the tube-level A being 5.0 cm higher than level B. The liquid supports a 20-cm high column of oil, between levels B and C, whose density is 320 kg/m3. The gauge pressure at level B is closest to
A. 630 Pa. B. 310 Pa. C. 470 Pa. D. 790 Pa. E. 940 Pa.
A jet airplane flies at a constant velocity through the air. Its jet engines exert a constant force forward on the plane that exactly balances the force of air friction exerted backward on the plane. These forces are equal in magnitude and opposite in direction. Do we know this because of Newton’s second law or Newton’s third law?
A. Newton’s second law B. Newton’s third law C. Both laws D. Neither (explain)
A 2.0-C charge moves with a velocity of (
m/s and experiences a magnetic force of 
N. The x component of the magnetic field is equal to zero. Determine the z component of the magnetic field.
A. ?3.0 T B. +3.0 T C. +5.0 T D. ?5.0 T E. +6.0 T
The length of a certain wire is kept same while its radius is doubled. What is the new resistivity of this wire?
A) It is increased by a factor of 2. B) It is increased by a factor of 4. C) It is reduced by a factor of 2. D) It is reduced by a factor of 4. E) It does not change.