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

Question 1

The banking angle for a properly banked curve does not depend on the mass of the car going over it.

Answer 1

True

Question 2

A body moving with constant speed cannot be accelerating.

Answer 2

False

Question 3

FIGURE 5-1
In Fig. 5-1, the block of mass m is at rest on an inclined plane that makes an angle θ with the horizontal. The force of static friction f must be such that

A)f > mg.
B)f > mg cosθ.
C)f > mg sinθ.
D)f = mg cosθ.
E)f = mg sinθ.

Answer 3

f = mg sinθ.

Question 4

A packing crate slides down an inclined ramp at constant velocity. Thus we can deduce that

A)a frictional force is acting on it.
B)a net downward force is acting on it.
C)a net upward force is acting on it.
D)it is not acted on by appreciable normal force.
E)it is not acted on by appreciable gravitational force.

Question 5

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

Question 6

When a curve is properly banked a passenger in a car traveling on it at the designed speed does not feel a lateral force.

Question 7

The force of friction between two surfaces is independent of the area of contact between the surfaces.

Question 8

The drag force is independent of the velocity of the object.

Question 9

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

Question 10

For uniform circular motion, the velocity and acceleration vectors are perpendicular to each other at every point in the path.

Question 11

Why does a cyclist tilt her bicycle on a curve?

Question 12

The banking of curves increases the chance of skidding.

Question 13

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

Question 14

Nonuniform circular motion occurs when the net force on an object is exerted toward the center of the circular path the object is following.

Question 15

Its more difficult to start moving a heavy carton from rest than it is to keep pushing it with constant velocity, because

A)The normal force is greater when the carton is at rest.
B) <
.
C)Initially, the normal force is not perpendicular to the applied force.
D) <
.
E) =
.

Question 16

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

Question 17

An airplane is flying with constant speed along a horizontal circle. Is the direction of its acceleration constant?

Question 18

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

Question 19

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

Question 20

Is it possible for an object moving with a constant speed to accelerate? Explain.

Question 21

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

A)kinetic friction
B)static friction
C)centripetal force
D)weight
E)tension

Question 22

When an object moves at constant speed on a circular path, which of the following is true?

A)A net force pointing along the direction of motion acts on the object.
B)A net force pointing along the opposite direction of motion acts on the object.
C)A net force pointing away from the center of the circle acts on the object.
D)A net force pointing towards the center of the circle acts on the object.
E)The net force acting on the object is zero.

Question 23

A 55.0-kg box rests on a horizontal surface. The coefficient of static friction between the box and the surface is 0.300. What horizontal force must be applied to the box for it to start sliding along the surface?

Question 24

FIGURE 5-1
What type of acceleration does an object moving with constant speed in a circular path experience?

A)free fall.
B)terminal acceleration.
C)constant acceleration.
D)linear acceleration.
E)centripetal acceleration.

Question 25

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 of the current acceleration of the object?

A)

B)

C)

D)

E)

Question 26

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?

A)0.375
B)0.600
C)0.420
D)0.625
E)0.700

Question 27

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?

A)to give the team better control, because they are able to see ahead of the turn
B)to prevent the bobsled from turning over
C)to take the turn at a faster speed
D)to take the turn at a slower speed
E)to reduce the g-force on them

Question 28

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

A)larger in magnitude the smaller the radius of the circle.
B)in the same direction as the velocity of the object.
C)smaller in magnitude the smaller the radius of the circle.
D)in the opposite direction of the velocity of the object.
E)zero.

Question 29

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?

Question 30

When an object experiences uniform circular motion, the direction of the net force is

A)in the same direction as the motion of the object.
B)in the opposite direction of the motion of the object.
C)is directed toward the center of the circular path.
D)is directed away from the center of the circular path.
E)is dependent on the speed of the object.

Question 31

Is it possible for an object moving around a circular path to have both centripetal and tangential acceleration?

A)No, because then the path would not be a circle.
B)No, an object can only have one or the other at any given time.
C)Yes, this is possible if the speed is constant.
D)Yes, this is possible if the speed is changing.

Question 32

When an object experiences uniform circular motion, the direction of the acceleration is

A)in the same direction as the velocity vector.
B)in the opposite direction of the velocity vector.
C)is directed toward the center of the circular path.
D)is directed away from the center of the circular path.
E)depends on the speed of the object.

Question 33

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

A)the acceleration is equal to g.
B)the force of air resistance is equal to zero.
C)the effect of gravity has died down.
D)the effect of gravity increases as he becomes closer to the ground.
E)the force of air resistance is equal to the weight of the parachutist.

Question 34

A car of mass m goes around a banked curve of radius r with speed v. If the road is frictionless due to ice, the car can still negotiate the curve if the horizontal component of the normal force on the car from the road is equal in magnitude to

A)mg/2.
B)mg.
C)mg sinθ .
D)mv²/r.
E)tan[v²/(rg)].

Question 35

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

A)It is moving in a straight line.
B)It is moving in a circle.
C)It is moving in a parabola.
D)It is moving in a hyperbola.
E)None of the above is definitely true all of the time.

Question 36

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)

B)

C)

D)

E)

Question 37

As a car drives with its tires rolling freely without any slippage, the type of friction acting between the tires and the road is

A)static friction.
B)kinetic friction.
C)a combination of static and kinetic friction.
D)neither static nor kinetic friction, but some other type of friction.
E)It is impossible to tell what type of friction acts in this situation.

Question 38

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

A)the viscosity of the fluid.
B)the size of the object.
C)the shape of the object.
D)all of the above choices.
E)none of the above choices.

Question 39

A 55-kg box rests on a horizontal surface. The coefficient of static friction between the box and the surface is 0.30. A 140-N force is applied to the box. What is the frictional force on the box?

Question 40

A car goes around a curve at a constant speed. What is the direction of the net force on the car?

A)toward the curve's center
B)away from the curve's center
C)toward the front of the car
D)toward the back of the car
E)the net force is zero

Question 41

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?

A)35.0°
B)13.5°
C)33.8°
D)56.2°
E)60.9°

Question 42

A car enters a 300-m radius flat curve on a rainy day when the coefficient of static friction between its tires and the road is 0.600. What is the maximum speed which the car can travel around the curve without sliding?

A)29.6 m/s
B)33.1 m/s
C)24.8 m/s
D)42.0 m/s
E)37.9 m/s

Question 43

FIGURE 5-5
A 4.00-kg block is sliding up the plane on a 30.0 degree incline as shown in Fig. 5-5. If the coefficient of kinetic friction between the block and the incline is 0.700, what will be the acceleration of the block if a 50.0-N horizontal force pushes on the block?

A)4.40 m/s² down the incline
B)12.5 m/s² up the incline
C)0.107 m/s² down the incline
D)10.8 m/s² up the incline
E)3.88 m/s² up the incline

Question 44

A 1000-kg car is picking up speed as it goes around a horizontal curve whose radius is 100 m. The coefficient of static friction between the tires and the road is 0.350. At what speed will the car begin to skid sideways?

A)9.25 m/s
B)23.6 m/s
C)34.3 m/s
D)35.0 m/s
E)18.5 m/s

Question 45

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?

A)1590 N
B)3430 N
C)3620 N
D)7240 N
E)5330 N

Question 46

FIGURE 5-5
A box is sliding down an incline tilted at an angle 14.0° above horizontal. The box is sliding down the incline at a speed of 1.70 m/s. The coefficient of kinetic friction between the box and the incline is 0.380. How far does the box slide down the incline before coming to rest?

A)1.16 m
B)2.33 m
C)1.78 m
D)0.720 m
E)The box does not stop. It accelerates down the plane.

Question 47

An airplane is flying with constant speed of 300 m/s along a horizontal circle with a radius of 15,000 m. If the lift force of the air on the wings is perpendicular to the wings, at what angle relative to the horizontal should the wings be banked?

A)15.1°
B)22.2°
C)31.5°
D)37.7°
E)63.0°

Question 48

FIGURE 5-5
A 4.00-kg block rests on a 30.0 degree incline as shown in Fig. 5-5. If the coefficient of static friction between the block and the incline is 0.700, with what magnitude force must a horizontal force act on the block to start it moving up the incline?

A)34.0 N
B)51.1 N
C)54.7 N
D)84.1 N
E)76.4 N

Question 49

A 600-kg car is going around a curve with a radius of 120 m that is banked at an angle of 25.0° with a speed of 30.0 m/s. The coefficient of static friction between the car and the road is 0.300. What is the force exerted by friction on the car?

A)1590 N
B)3430 N
C)7240 N
D)7820 N
E)795 N

Question 50

A car drives over a hilltop that has a radius of curvature 120 m at the top of the hill. At what speed would the car be traveling when it tires just barely lose contact with the road when the car is at the top of the hill?

A)45.5 m/s
B)41.8 m/s
C)34.3 m/s
D)22.2 m/s
E)27.6 m/s

Question 51

A ball is tied to the end of a cable of negligible mass. The ball is spun in a circle with a radius 2.00 m making 0.700 revolutions per second. What is the centripetal acceleration of the ball?

A)67.9 m/s
B)38.7 m/s²
C)29.3 m/s
D)14.8 m/s
E)74.2 m/s

Question 52

A 2-kg ball is moving with a constant speed of 5 m/s in a horizontal circle whose radius is 50 cm. What is the acceleration of the ball?

A)0 m/s²
B)10 m/s²
C)20 m/s²
D)50 m/s²
E)500 m/s²

Question 53

FIGURE 5-5
A 50.0-kg block is being pulled up a 13.0° slope by a force of 250 N which is parallel to the slope. The coefficient of kinetic friction between the block and the slope is 0.200. What is the acceleration of the block?

A)0.528 m/s²
B)0.158 m/s²
C)0.833 m/s²
D)0.983 m/s²
E)0.260 m/s²

Question 54

A car travels around 200 m radius flat curve at 40 m/s at constant speed. What is the minimum static coefficient of friction which allows it to travel at this speed without sliding?

A)1.23
B)0.815
C)0.736
D)0.952
E)0.662

Question 55

A child pulls a 3.00-kg sled across level ground at constant velocity with a light rope that makes an angle 34.0° above horizontal. The tension in the rope is 5.00 N. Assuming the acceleration of gravity is 9.81 m/s², what is the coefficient of friction between the sled and the ground?

A)0.156
B)0.188
C)0.0441
D)0.0851
E)0.103

Question 56

A 600-kg car is going around a curve with a radius of 120 m that is banked at an angle of 20° with a speed of 24.5 m/s. What is the minimum coefficient of static friction required for the car not to skid?

A)0.12
B)0.24
C)0.36
D)0.48
E)0.60

Question 57

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?

A)16.2 N
B)54.9 N
C)21.1 N
D)23.5 N
E)78.5 N

Question 58

FIGURE 5-6
Two masses are connected by a string which goes over an ideal pulley as shown in Fig. 5-6. 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 kinetic friction between block A and the plane is 0.400. Block B has a mass of 2.77 kg. What is the acceleration of the blocks?

A)0.392 m/s²
B)1.96 m/s²
C)3.12 m/s²
D)5.35 m/s²
E)0 m/s²

Question 59

A 2-kg ball is moving with a constant speed of 5 m/s in a horizontal circle whose radius is 50 cm. What is the magnitude of the net force on the ball?

A)0 N
B)20 N
C)40 N
D)50 N
E)100 N

Question 60

A child stands on a playground merry-go-round a distance of 1.50 m from the rotation axis. The coefficient of static friction between the child's shoes and the surface of the merry-go-round is 0.700. Assuming the acceleration of gravity is 9.81 m/s², what is the maximum constant angular speed of the merry-go-round for which the child will not start to slide?

A)6.45 rad/s
B)1.32 rad/s
C)2.14 rad/s
D)4.58 rad/s
E)8.32 rad/s

Question 61

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

Question 62

What is the terminal velocity of a 6.00-kg mass object in falling with a drag force with a magnitude that depends on speed, v, as F_drag = (30.0 N∙s/m)v?

A)1.96 m/s
B)41.9 m/s
C)24.2 m/s
D)12.6 m/s
E)62.2 m/s

Question 63

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)110 m/s
B)157 m/s
C)91.0 m/s
D)172 m/s
E)108 m/s

Question 64

A 1.20-kg ball is hanging on the end of a rope. The rope makes an angle 25.0° from the vertical when a 15.0 m/s horizontal wind blows. If the wind's force on the rope is negligible, what is the drag force on the ball?

A)32.3 N
B)24.1 N
C)3.68 N
D)5.49 N
E)11.8 N

Question 65

The magnitude of the drag force on a 20.0-kg object is proportional to its speed. The object has a terminal velocity 80 m/s. What is the magnitude of the drag force on the object when it is falling with a speed 30 m/s?

A)196 N
B)7.50 N
C)15.0 N
D)73.6 N
E)42.7 N

Question 66

What is the terminal velocity of an 80.00-kg mass object in falling with a drag force with a magnitude that depends on speed, v, as F_drag = (12.0 N∙s/m)v + (4.00 N∙s/m)v²?

A)6.45 m/s
B)72.2 m/s
C)34.2 m/s
D)12.6 m/s
E)47.3 m/s

Question 67

A race car enters a flat 200-m radius curve at a speed of 20.0 m/s while increasing its speed at a constant 2.00 m/s². If the coefficient of static friction is 0.700, what will the speed of the car be when the car begins to slide?

A)36.2 m/s
B)24.3 m/s
C)37.1 m/s
D)28.7 m/s
E)31.5 m/s

Question 68

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)38.1 m/s
B)55.9 m/s
C)28.8 m/s
D)65.4 m/s
E)43.2 m/s