PRACTICE TEST 3
69. The cor wer is (C) corrrect ans answ (C). The problem may be solved in several ways. Perhaps the best solution is a little thought. The potential energy and the kinetic energy are equal to one another when the object has fallen half the distance to the ground, or 10 m. All we have to do now is treat the problem as a free fall problem by restating the situation a little. The velocity of an object that starts from rest and free falls 10 m? The solution is found by v f = 2 gs . 70. The cor wer is (C) corrrect ans answ (C). When the variable resistor is moved toward the right, more of the resistance value of the variable resistor is bypassed which means there is less resistance in the circuit. A decrease in the resistance of a circuit allows more current to flow (Ohm’s Law). Since there is more current flowing in the circuit the fan has more current flowing through it too, and the fan runs faster. 71. The cor wer is (E) corrrect ans answ (E). The pulse shown strikes a fixed barrier. The wave is reflected and inverted. 72. The cor wer is (C) corrrect ans answ (C). All forces occur in pairs, are equal in magnitude and oppositely directed. The pairs of forces are the ball on the window, and the window on the ball, which are equal and opposite. 73. The cor wer is (C) corrrect ans answ (C). When the voltage is disconnected there is a small lag time between the disconnection of the current and the ceasing of the flow because the magnetic field, which is induced into the wires, collapses. This produces a current flow that causes the spark. 74. The cor wer is (D) corrrect ans answ (D). An electric current is passed through an electromagnet or rotor, which causes it to spin within an applied magnetic field. The spinning rotor is the source of mechanical energy that is derived from electrical energy. 75. The cor wer is (C) corrrect ans answ (C). The two wires have a magnetic field around them that is caused by the current in the wires. The two fields are in opposition, which weakens them on the sides closest to one another. This allows the unweakened field on the other (outside) of the wires to push the two wires together.
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Peterson’s SAT II Success: Physics