A rock attached to a string swings in a vertical circle. Which free-body diagram could correctly describe the force(s) on the rock when the string is in one possible horizontal position, where
is the normal force,
is weight, and 
is tension?
a.
b.
c.
d.
e.
c
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Using 0.0200 mol of an ideal monatomic gas, an isochoric process from A (230 kPa, 1.00 L) to B (98 kPa, 1.00 L) results in what change in internal energy?
A. -200 J B. +200 J C. -375 J D. +375 J
The coefficient of linear expansion of steel is 12 × 10-6 K-1. What is the change in length of a 25-m steel bridge span when it undergoes a temperature change of 40 K from winter to summer?
A) 1.2 cm B) 1.4 cm C) 1.6 cm D) 1.8 cm E) 2.0 cm
A 500-eV electron and a 300-eV electron trapped in a uniform magnetic field move in circular paths in a plane perpendicular to the magnetic field. What is the ratio of the radii of their orbits?
a. 2.8 b. 1.7 c. 1.3 d. 4.0 e. 1.0
A proton moving at 6.0 × 10^4 m/s is projected at an angle of 30° above a horizontal plane. If an electric field of 400 N/C is acting down, how long does it take the proton to return to the horizontal plane? (Hint: Ignore gravity. mproton = 1.67 × 10^-27 kg, qproton = 1.6 × 10^-19 C)
a. 7.8 × 10^-6 s c. 7.8 × 10^-7 s b. 1.6 × 10^-6 s d. 3.9 × 10^-6 s