A rock is thrown from the edge of the top of a 100-ft tall building at some unknown angle above the horizontal. The rock strikes the ground a horizontal distance of 160 ft from the base of the building 5.0 s after being thrown. Assume that the ground is level and that the side of the building is vertical. Determine the speed with which the rock was thrown
a. 72 ft/s
b. 77 ft/s
c. 68 ft/s
d. 82 ft/s
e. 87 ft/s
C
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Parallel Wires: An object is hung using a metal spring. If now a current is passed through the spring, what will happen to this system?
A. The spring will contract, raising the weight. B. The spring will extend, lowering the weight. C. The weight will not move. D. The spring will begin to swing like a pendulum. E. None of these are true.
An 800-kHz radio signal is detected at a point 8.5 km distant from a transmitter tower. The electric field amplitude of the signal at that point is 0.90 V/m
Assume that the signal power is radiated uniformly in all directions and that radio waves incident upon the ground are completely absorbed. What is the average electromagnetic energy density at that point? (c = 3.0 × 108 m/s, ?0 = 4? × 10-7 T ? m/A, ?0 = 8.85 × 10-12 C2/N ? m2) A) 3.6 pJ/m3 B) 5.1 pJ/m3 C) 7.2 pJ/m3 D) 10 pJ/m3 E) 14 pJ/m3
Heat normally flows from objects of high
A) internal energy to objects of low internal energy. B) temperature to objects of low temperature. C) both of these D) neither of these
Galaxies seem to be made mostly of dark matter. One type of evidence for this comes from observations of
A) the redshift in the light from the explosions of distant supernovas. B) the redshift in the light from the earliest galaxies in the universe. C) Both of the above. D) the speeds at which gas clouds orbit the centers of galaxies. E) distant quasars.