Practice Exam #2. Please bring this with you to the SI review session on Monday, March 31. Please do NOT look past this page until then.

Transcription

1 Exam Review Sections Supplemental Instruction Iowa State University Leader: Brian Course: PHYS 221 Instructor: Ho Date: 03/31/2014 Practice Exam #2 Please bring this with you to the SI review session on Monday, March 31. Please do NOT look past this page until then. 1

2 1. A force parallel to the x-axis acts on a particle moving along the x-axis. This force produces potential energy U(x), given by U(x) = ax^4, where a = 1.20 J/m^4. What is the force when the particle is at x = m? a m in the x direction b m in the -x direction c m in the x direction d m in the -x direction 2. The plot a right shows the potential energy U of a particle moving along the x-axis as a function of the position x of the particle. The position of stable equilibrium of the particle is at a. -3 m b. -1 m c. 1 m d. 3m 3. Block A (mass = 2.00 kg) and Block B (mass = kg) move on a frictionless horizontal surface. Block B is initially at rest and Block A moves toward it at 2.00 m/s. Both blocks are equipped with ideal spring bumpers and the collision is head on, so the motion before and after the collision is along a straight line. What is the velocity of each block after they move apart? a. Block A m/s in the x direction, Block B m/s in the x direction b. Block A 1.33 m/s in the x direction, Block B m/s in the x direction c. Block A 1.33 m/s in the -x direction, Block B m/s in the x direction d. Block A 1.67 m/s in the -x direction, Block B m/s in the -x direction 2

3 4. The diameter of planet X is approximately 2370 km, and the diameter of one of its moons is approximately 1250 km. For this problem we consider their average densities equal. Without regard to the planet s remaining moons and assuming that the center-to-center distance between the planet and the moon is exactly 19,700 km, what is the center of mass of this system relative to planet X? a. 4.55*10 ^3 km b. 2.52*10 ^3 km c. 2.56*10 ^3 km d. 4.44*10 ^3 km 5. A rod of mass 1.0 kg and length 0.5 m is connected on one end to the ceiling by a frictionless hinge. It is released from rest when it is in the horizontal position. What is its angular velocity when it is vertical? a rad/s b rad/s c rad/s d rad/s θ 6. In the system shown, a 12.0 kg mass is released from rest and falls, causing the uniform 10.0 kg cylinder with 30.0 cm diameter to turn about a frictionless axel at its center. How far must the mass descend in order to give the cylinder 480 J of kinetic energy? a m b. 4.6 m c m d m 7. A m in diameter drum with negligible mass is attached to the shaft in an industrial motor. The motor s power output is used to raise a weight hanging from a rope attached to the drum. How heavy a weight may the motor lift at constant speed? a N b N c N d N 3

4 kg diver stands on the edge of a uniform diving board of mass kg and length 4.0 m. The diving board is supported at two points as shown. What is the magnitude and direction of the force at point A, in N? (4.0 m) a N, up b N, up c N, down d N, down B A (1.0 m) kg, 0.5 m long bar has a small kg mass glued to its left end and a small kg mass glued to its right end. The 2 masses may be treated as point masses. You want to balance the system horizontally on a fulcrum placed just under its center of gravity. How far from its left end should the fulcrum be placed? a m b. 1.4 m c m d m 10. Find the force acting on the weightless horizontal strut by the wall. a. 500 N b. 525 N c. 330 N d. 400 N 3 m 5 m 4 m In a materials testing laboratory, a wire made from a new alloy is found to break when a tensile force of 90.8 N is applied perpendicular to each end. If the wire s diameter = m, what is the breaking stress of the alloy? a. 4.66*10^7 Pa b. 3.41*10^7 Pa c. 6.67*10^7 Pa d. 2.99*10^7 Pa 4

5 12. Neutron stars have about the same mass as our sun but a much smaller diameter. If you weigh 675 N on the earth, what would you weigh at the surface of a neutron star which has a mass identical to the mass of our sun but a diameter of only 20 km? You may use 1.99 * 10^30 kg as the mass of our sun. a. 4.99*10^4 N b. 3.04*10^13 N c. 9.16*10^13 N d. 9.10*10^4 N 13. A particle of mass 3m is located 1.00 m from a particle of mass m. Where along an axis plotted directly through the masses centers should you place a mass M, so that the net gravitational force on M from the other masses is exactly zero? a m from 3m b m from m c m from 3m d m from M 5