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Unformatted text preview: huynh (hph268) HW #3 clark (56485) 1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points An empty office chair is at rest on a floor. Consider the following forces: 1. A downward force of gravity, 2. An upward force exerted by the floor, and 3. A net downward force exerted by the air. Which of the forces is (are) acting on the office chair? 1. None of the forces act on the chair. (Since the chair is at rest there are no forces acting upon it.) 2. 1 and 2. correct 3. 2 and 3. 4. 1 only. 5. 1, 2, and 3. Explanation: The forces acting on the chair are gravity and buoyant force exerted by the air in up- ward direction, as well as force of the floor reaction pointing upward. 002 10.0 points Despite a very strong wind, a tennis player manages to hit a tennis ball with her racquet so that the ball passes over the net and lands in her opponents court. Consider the following forces: 1. A downward force of gravity, 2. A force by the hit, and 3. A force exerted by the air. Which of the above forces is (are) acting on the tennis ball after it has left contact with the racquet and before it touches the ground? 1. 2 and 3. 2. 1 and 3. correct 3. 1 only. 4. 1 and 2. 5. 1, 2, and 3. Explanation: The forces acting on the tennis ball after it has left contact with the racquet are gravity and air resistance. A force by the hit is no longer acting on the ball. 003 10.0 points A toy car is given a quick push so that it moves up an inclined ramp. After it is released, it moves up, reaches its highest point and moves back down again. Friction is so small it can be ignored. What net force acts on the car? 1. Net increasing force down the ramp 2. Net constant force down the ramp cor- rect 3. Net increasing force up the ramp 4. Net force of zero 5. Net decreasing force down the ramp 6. Net decreasing force up the ramp 7. Net constant force up the ramp Explanation: The net force is the component of gravity along the incline; it is constant and acts down the ramp. 004 10.0 points What is the net force on a Mercedes convert- ible traveling along a straight road at a steady speed of 100 km/h? huynh (hph268) HW #3 clark (56485) 2 1. 200 N 2. All are wrong. 3. 0 N correct 4. 100 N 5. 10 N Explanation: The net force is zero because the Mercedes is traveling at constant velocity, which means with zero acceleration. 005 10.0 points Suppose a cart is being moved by a certain net force. If a load is added to the cart so its mass is doubled, by what factor does its acceleration change? 1. 0.5 correct 2. 2 3. 4 4. 0.625 5. 0.25 6. 1 7. 0.333 8. 3 9. 0.2 10. 1.5 Explanation: F net = ma net The mass is doubled, but the net force can- not change, so multiply the right side by a clever form of 1 = 2 parenleftbigg 1 2 parenrightbigg : F net = (2 m ) parenleftbigg 1 2 a parenrightbigg and the acceleration must then be halved....
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