20. An electron has been accelerated by a potential difference of 100 V. If its position is known to have an uncertainty of 1 nm, what is the percent uncertainty × 100% of the electron?
(A) 1%
(B) 8%
(C) 10%
(D) ＞＞10%
(E) 5%

1. The initial speed of a cannon ball is 0.20 km/s. If the ball is to strike a target that is at a horizontal distance of 3.0 km from the cannon, what is the minimum time of flight for the ball? (A) 16 s (B) 35 s (C) 28 s (D) 4 s (E) 49 s

2. Two blocks connected by a string are pulled across a horizontal surface by a force applied to one of the blocks, as shown in right. The coefficient of kinetic friction between the blocks and the surface is 0.25. If each block has an acceleration of 2.0 m/s² to the right, what is the magnitude F of the applied force? (1.0 kg and 3.0 kg blocks, F at 60°) (A) 12 N (B) 25 N (C) 34 N (D) 43 N (E) 7 N

3. A force acting on an object moving along the x axis is given by Fx = (14x − 3.0x²) N, where x is in m. How much work is done by this force as the object moves from x = −1 m to x = +2 m? (A) +12 J (B) +28 J (C) +40 J (D) +42 J (E) −28 J

4. A 3.50-kg block is pulled along a moving conveyor belt at a constant speed of 0.500 m/s relative to a stationary observer, while the belt moves at a constant speed of 0.200 m/s in the same direction. If the coefficient of kinetic friction is 0.400, the magnitude of the mechanical energy dissipated, in J, caused by the force of friction on the block in 8.00 s is (A) 5.6 (B) 22.0 (C) 32.9 (D) 54.8 (E) 76.8

5. A 3.0-kg block is on a horizontal surface. The block is at rest when, at t = 0, a force (magnitude P = 12 N) acting parallel to the surface is applied to the block, causing it to accelerate. The coefficient of kinetic friction between the block and the surface is 0.20. At what rate is the force P doing work on the block at t = 2.0 s? (A) 58 W (B) 49 W (C) 39 W (D) 64 W (E) 18 W

6. A mass m = 4.0 kg is connected, as shown, by a light cord to a mass M = 6.0 kg, which slides on a smooth, horizontal surface. The pulley rotates about a frictionless axle and has a radius R = 0.12 m and a moment of inertia I = 0.090 kg·m². The cord does not slip on the pulley. What is the magnitude of the acceleration of m? (A) 2.4 m/s² (B) 3.8 m/s² (C) 5.2 m/s² (D) 4.5 m/s² (E) 1.1 m/s²

7. An airplane traveling at half the speed of sound emits sound at a frequency of 5000 Hz. At what frequency does a stationary listener hear the sound as the plane approaches, and after it passes by? Assume the airplane is not flying very high. (A) 5000 Hz, 6000 Hz (B) 3000 Hz, 6666 Hz (C) 4000 Hz, 2333 Hz (D) 10000 Hz, 3333 Hz (E) 7000 Hz, 9000 Hz

8. A 100-g cube of ice is heated from −120 °C to +120 °C. In which of the following processes is the greatest amount of energy absorbed by this material? (A) warming ice to the melting point (B) melting the ice to become water (C) warming the resulting water (D) vaporizing the water to become steam (E) heating the steam

9. For the same temperature increase in a system, the change in entropy, ΔS, is largest in a reversible (A) constant-volume process. (B) constant-pressure process. (C) adiabatic process. (D) process in which no heat is transferred. (E) process in which no work is performed.

10. Two tanks of gas, one of hydrogen, H₂, and one of helium, He, contain equal masses of gas. The gram-molecular mass of He is twice that of H₂. Both tanks of gas are at the same temperature, 293 K. Which statement(s) below is(are) correct when we ignore vibrational motion? (A) The total internal energy of the hydrogen is the same as that of the helium. (B) The total internal energy of the hydrogen is 167 times that of the helium. (C) The total internal energy of the helium is 1.67 times that of the hydrogen. (D) The total internal energy of the hydrogen is 3.33 times that of the helium. (E) The total internal energy of the helium is 3.33 times that of the hydrogen.

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