Q: A 2 kg block is at rest on a horizontal surface. The coefficient of static friction is $$0.5. $$What is the maximum horizontal force that can be applied before the block starts to move?

$$F_{\text{max}} = 19.6\,\text{N}$$

Question 1

A 10 kg box is pulled across a horizontal floor with a constant velocity. If the coefficient of kinetic friction between the box and the floor is $$\mu_k = 0.4$$, what is the magnitude of the pulling force?

Accepted Answer

$$F = 39.2\,	ext{N}$$

Question 2

Which of the following statements about static friction is correct?

Accepted Answer

Static friction can have any value from zero up to a maximum of $$\mu_s N.$$

Question 3

A block of mass $$m is $$connected by a light string over a frictionless pulley to a hanging mass $$M. If$$ $$M \u003e m$$, what is the acceleration of the system?

Accepted Answer

$$a = \dfrac{M - m}{M + m}g$$

Question 4

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

Accepted Answer

$$\mu_s = \dfrac{v^2$}{rg}$$

Question 5

A spring stretches by 0.2 m when a force of 10 N is applied. What is the spring constant $$k$$?

Accepted Answer

$$k = 50\,	ext{N/m}$$

Question 6

A 5 kg object is suspended by a rope. What is the tension in the rope if the object is at rest?

Accepted Answer

$$T = 49\,	ext{N}$$

Question 7

A 2 kg block is at rest on a horizontal surface. The coefficient of static friction is $$0.5. $$What is the maximum horizontal force that can be applied before the block starts to move?

Accepted Answer

$$F_{	ext{max}} = 19.6\,	ext{N}$$

Question 8

Which of the following best describes the force responsible for keeping a satellite in circular orbit around Earth?

Accepted Answer

Centripetal force provided by gravity

Question 9

A 3 kg object moves in a circle of radius 2 m at a constant speed of 4 m/s. What is the magnitude of the required centripetal force?

Accepted Answer

$$F = 24\,	ext{N}$$

Question 10

A box is pulled at constant speed across a rough surface. If the normal force doubles, what happens to the force of kinetic friction?

Accepted Answer

It doubles.

Question 11

A block is at rest on an inclined plane. Which force is responsible for preventing the block from sliding down?

Accepted Answer

Static friction

Question 12

A 2 kg mass is attached to a spring with $$k = 100\,	ext{N/m}. $$How far does the spring stretch under the weight of the mass?

Accepted Answer

$$0.02\,	ext{m}$$

Question 13

Which of the following is true for an object in translational equilibrium?

Accepted Answer

The net force on the object is zero.

Question 14

A 1 kg block is connected to a 2 kg block by a massless string over a frictionless pulley. What is the acceleration of the system?

Accepted Answer

$$a = 3.27\,	ext{m/s}^2$$

Question 15

A ball is whirled in a horizontal circle at constant speed. Which statement is correct?

Accepted Answer

The acceleration is directed toward the center.

Question 16

A 4 kg object is attached to a string and swung in a vertical circle of radius 2 m. What is the tension in the string at the lowest point if the speed is 6 m/s?

Accepted Answer

$$T = 118.4\,	ext{N}$$

Applications of Newton’s Laws: Friction, Strings, Equilibrium, Connected Objects, and Circular Motion

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