Q: On a banked curve, what is the formula for the banking angle $$\theta so $$that no friction is required for a car to round the curve of radius $$r at $$speed $$v$$?

$$\tan \theta = \dfrac{v^2$}{g r}$$

Question 1

Which fundamental force is responsible for friction between two solid surfaces sliding past each other?

Accepted Answer

The electromagnetic force

Question 2

A 10.0-kg box rests on a horizontal floor. The coefficient of static friction is 0.40 and the coefficient of kinetic friction is 0.30. If a horizontal force of 38 N is applied, what is the frictional force acting on the box?

Accepted Answer

$$f_{fr} = 29.4\,\mathrm{N}$$

Question 3

Which equation correctly expresses the maximum static frictional force between two surfaces?

Accepted Answer

$$F_{fr} \leq \mu_s F_N$$

Question 4

A skier descends a slope at constant speed. What does this imply about the coefficient of kinetic friction $$\mu_k$$?

Accepted Answer

$$\mu_k = 	an 	heta$$

Question 5

A 2.50-kg block rests on a ramp. If the coefficient of static friction is 0.350, what is the maximum angle $$	heta$$ the ramp can make with the horizontal before the block starts to slide?

Accepted Answer

$$	heta = \arctan(0.350)$$

Question 6

Which statement about the direction of frictional force is correct?

Accepted Answer

It is always opposite to the direction of motion.

Question 7

A 0.150-kg ball is attached to a string and revolves in a horizontal circle of radius 0.600 m at 2.00 revolutions per second. What is the centripetal acceleration?

Accepted Answer

$$a_c = 57.0\,\mathrm{m/s^2$}$$

Question 8

Which formula gives the magnitude of centripetal acceleration for an object moving in a circle of radius $$r at $$speed $$v$$?

Accepted Answer

$$a_c = \dfrac{v^2$}{r}$$

Question 9

A car of mass $$m$$ rounds a flat curve of radius $$r at $$speed $$v. $$What is the minimum coefficient of static friction $$\mu_s$$ required to prevent skidding?

Accepted Answer

$$\mu_s = \dfrac{v^2$}{g r}$$

Question 10

On a banked curve, what is the formula for the banking angle $$	heta so $$that no friction is required for a car to round the curve of radius $$r at $$speed $$v$$?

Accepted Answer

$$	an 	heta = \dfrac{v^2$}{g r}$$

Question 11

A ball is swung in a vertical circle. What is the minimum speed at the top of the circle to keep the string taut?

Accepted Answer

$$v_{min} = \sqrt{g r}$$

Question 12

When a car rounds a curve and the tires begin to slip, which type of friction acts and what is the consequence?

Accepted Answer

Kinetic friction acts and the car is more likely to skid.

Question 13

A falling object reaches terminal velocity when:

Accepted Answer

The drag force equals the gravitational force.

Question 14

For small velocities, the drag force $$F_{drag} on an $$object moving through a fluid is:

Accepted Answer

$$F_{drag} \propto v$$

Question 15

A box is held against a rough vertical wall by pressing horizontally. What force prevents the box from sliding down?

Accepted Answer

The frictional force between the box and the wall

Question 16

A 10.0-kg box is pulled along a horizontal surface by a force of 40.0 N applied at a $$30.0^\circ$$ angle above the horizontal. The coefficient of kinetic friction is 0.30. What is the acceleration of the box?

Accepted Answer

$$a = 1.36\,\mathrm{m/s^2$}$$

Question 17

Which of the following statements about coefficients of friction is correct?

Accepted Answer

Coefficients of friction are nearly independent of the area of contact.

Question 18

In uniform circular motion, the net force acting on the object is always:

Accepted Answer

Directed toward the center of the circle

Using Newton's Laws: Friction, Circular Motion, Drag Forces

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