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Exam 5: Using Newtons Laws: Friction, Circular Motion, Drag Forces

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Question 1

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The coefficient of static friction is always larger than the coefficient of kinetic friction.

A) True
B) False

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Question 2

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FIGURE 5-7 -A ship is being pulled through a harbor by two tug boats at constant velocity as shown in Fig. 5-7. The lines attached to the two tug boats have the same tension, 200,000 N. The lines each make an angle 28.0° to the direction the ship is being towed. What is the magnitude of the drag force on the ship?

A) 177 × 10⁵ N
B) 1.88 × 10⁵ N
C) 93.9 × 10⁴ N
D) zero
E) 3.53 × 10⁵ N

F) C) and D)
G) B) and C)

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Question 3

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The force of static friction between two surfaces is parallel to the surface of contact, and in the direction that opposes relative motion.

FIGURE 5-4 -A 4.00-kg block rests between the floor and a 3.00-kg block as shown in Fig. 5-4. The 3.00-kg block is tied to a wall by a horizontal rope. If the coefficient of static friction is 0.800 between each pair of surfaces in contact, what force must be applied horizontally to the 4.00-kg block to make it move?

Consider a particle moving with constant speed such that its acceleration of constant magnitude is always perpendicular to its velocity.

A 600-kg car is going around a banked curve with a radius of 110 m at a speed of 27.5 m/s. What is the appropriate banking angle so that the car stays on its path without the assistance of friction?

The banking angle in a turn on the Olympic bobsled track is not constant, but increases upward from the horizontal. Coming around a turn, the bobsled team will intentionally "climb the wall," then go lower coming out of the turn. Why do they do this?

In problems involving a slope or inclined plane, the normal force is always perpendicular to the slope or the plane.

An object is acted on by a drag force with a magnitude that is proportional to the speed. The object accelerates downward at 3.00 m/s² when it is falling with a speed 20.0 m/s. What is the terminal speed of the object as it is falling?

A 60.0-kg mass person wishes to push a 100-kg mass box across a level floor. The coefficient of static friction between the person's shoes and the floor is 0.700. What is the maximum coefficient of static friction between the box and the floor such that the person can push horizontally on the box and cause it to start moving?

FIGURE 5-1 -For an object that travels at a fixed speed along a circular path, the acceleration of the object is

It is often easier to keep a heavy object sliding than it is to start it sliding in the first place.

When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal velocity. This means that

For very small objects at very low speeds, the drag force is directly proportional to the magnitude of the velocity. The proportionality constant depends on

FIGURE 5-3 -Two masses are connected by a string which goes over an ideal pulley as shown in Fig. 5-3. Block A has a mass of 3.00 kg and can slide along a rough plane inclined 30.0° to the horizontal. The coefficient of static friction between block A and the plane is 0.400. What mass should block B have in order to start block A sliding up the ramp?

A 30.0-kg object has a drag force with a magnitude proportional to the square of its speed. The object falls with an acceleration 4.00 m/s² downward when it is falling downward at 70.0 m/s. What is its terminal velocity?

A 600-kg car is going over a curve with a radius of 120 m that is banked at an angle of 25° with a speed of 30.0 m/s. The coefficient of static friction between the car and the road is 0.30. What is the normal force exerted by the road on the car?

What force is needed to make an object move in a circle?

FIGURE 5-2 -Fig. 5-2 indicates the current position of an object traveling at constant speed clockwise around the circle. Which arrow best represent the direction the object would travel if the centripetal force was suddenly reduced to zero?

A net horizontal force is required for a body to move in a horizontal circle.