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**Related to previous class: **

A destroyer simultaneously fires two shells with the same initial speed at two different enemy ships. The shells follow the trajectories shown. Which ship gets hit first. D The vertical component of the velocity is 0, but the horizontal component is still the same as the initial one. Acceleration is always downward g. A) Enemy 1 B) Enemy 2 C) They are both hit at the same time

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**Related to previous class: **

A destroyer simultaneously fires two shells with the same initial speed at two different enemy ships. The shells follow the trajectories shown. Which ship gets hit first. D The vertical component of the velocity is 0, but the horizontal component is still the same as the initial one. Acceleration is always downward g. A) Enemy 1 B) Enemy 2 C) They are both hit at the same time

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Free Body Diagrams For any complicated situation, Isolate each object; Draw all forces acting on it; Use for each object.

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Statics For any complicated situation, Isolate each object; Draw all forces acting on it; Use and for each object.

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Statics For any complicated situation, Isolate each object; Draw all forces acting on it; Use and for each object. Example: calculate F2 and F1 as a function of mg, L and x2.

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Statics For any complicated situation, Isolate each object; Draw all forces acting on it; Use and for each object. Example: calculate F2 and F1 as a function of mg, L and x2. Forces: Torques:

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**A (static) mobile hangs as shown**

A (static) mobile hangs as shown. The rods are massless and have lengths as indicated. The mass of the bottom right ball is 1kg. What is the total mass of the mobile? 4 kg 5 kg 6 kg 7 kg 8 kg

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**A (static) mobile hangs as shown**

A (static) mobile hangs as shown. The rods are massless and have lengths as indicated. The mass of the bottom right ball is 1kg. What is the total mass of the mobile? 4 kg 5 kg 6 kg 7 kg 8 kg

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N5T.2 A person would like to pull a car out of a ditch. This person ties one end of a chain to the car’s bumper and wraps the other end around a tree so that the chain is taut. The person then pulls on the chain perpendicular to its length, as shown in the picture. The magnitude of the force that the chain exerts on the car in this situation is: Much smaller than the force the person exerts on the chain. About equal to the force the person exerts on the chain. Much bigger than the force the person exerts on the chain.

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N5T.2 A person would like to pull a car out of a ditch. This person ties one end of a chain to the car’s bumper and wraps the other end around a tree so that the chain is taut. The person then pulls on the chain perpendicular to its length, as shown in the picture. The magnitude of the force that the chain exerts on the car in this situation is: Much smaller than the force the person exerts on the chain. About equal to the force the person exerts on the chain. Much bigger than the force the person exerts on the chain.

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N5T.3 The lid of a grand piano is popped open as shown. Which arrow most closely approximates the direction of the force that the hinge exerts on the lid?

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N5T.3 The lid of a grand piano is popped open as shown. Which arrow most closely approximates the direction of the force that the hinge exerts on the lid?

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N5T.4 Imagine that a helicopter’s rotor spins clockwise. The helicopter engine must continually exert a torque on the rotor to keep it spinning against the drag that the air exerts on the rotor. Note that a helicopter is usually designed so that its center of mass is directly under the rotor. In order for the helicopter to hover motionless in the air, a small rotor at the helicopter’s tail is necessary. As viewed by someone looking at the tail from the helicopter’s front, the small rotor must blow air: To the left. To the right. Vertically upward. Vertically downward. In some combination of these directions.

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N5T.4 Imagine that a helicopter’s rotor spins clockwise. The helicopter engine must continually exert a torque on the rotor to keep it spinning against the drag that the air exerts on the rotor. Note that a helicopter is usually designed so that its center of mass is directly under the rotor. In order for the helicopter to hover motionless in the air, a small rotor at the helicopter’s tail is necessary. As viewed by someone looking at the tail from the helicopter’s front, the small rotor must blow air: To the left. To the right. Vertically upward. Vertically downward. In some combination of these directions.

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N5T.5 A board of mass m lies on the ground. What is the magnitude of the force that you would have to exert to lift one end of the board barely off the ground (assuming that the other end still touches the ground)? 2mg mg The answer depends on the length of the board. mg/2

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N5T.5 A board of mass m lies on the ground. What is the magnitude of the force that you would have to exert to lift one end of the board barely off the ground (assuming that the other end still touches the ground)? 2mg mg The answer depends on the length of the board. mg/2

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N5T.6 Imagine that you continue to lift the board described in problem N5T.5. Assume that the force you exert is always perpendicular to the board, and that the board always remains on the ground. What happens to the magnitude of the force you exert on the end as the angle between the board and the ground increases? It: Increases. Decreases. Remains the same.

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N5T.6 Imagine that you continue to lift the board described in problem N5T.5. Assume that the force you exert is always perpendicular to the board, and that the board always remains on the ground. What happens to the magnitude of the force you exert on the end as the angle between the board and the ground increases? It: Increases. Decreases. Remains the same.

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**Consider the ladder in the figure**

Consider the ladder in the figure. When is the tension in the string maximal? When the person is at the top (x=0). When the person is at the bottom (x=L sina). Somewhere in between x=0 and x=L sina. Independent on where person is.

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**Consider the ladder in the figure**

Consider the ladder in the figure. When is the tension in the string maximal? When the person is at the top (x=0). When the person is at the bottom (x=L sina). Somewhere in between x=0 and x=L sina. Independent on where person is.

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Problems Chapter 4,5.

Problems Chapter 4,5.

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