Q: A block slides down an incline with friction. The coefficient of kinetic friction is $$\mu_k$$, the incline angle is $$\theta$$, and $$g is $$gravity. What is the acceleration?

$$g(\sin\theta - \mu_k\cos\theta)$$

Question 1

A 10 kg block rests on a horizontal surface. The coefficient of static friction is 0.5 and the coefficient of kinetic friction is 0.4. If a 10 N horizontal force is applied, what is the magnitude and type of friction force acting on the block?

Accepted Answer

$$10\ \mathrm{N}$$, static friction

Question 2

A 1000 kg car travels around a flat curve of radius $$100\ \mathrm{m} at$$ $$20\ \mathrm{m/s}. $$What is the minimum coefficient of static friction required to prevent the car from sliding?

Accepted Answer

$$0.41$$

Question 3

A block of mass $$m$$ slides down a frictionless incline at angle $$	heta. $$What is the acceleration of the block?

Accepted Answer

$$g\sin	heta$$

Question 4

A 2 kg object is placed on a rotating disk at a radius of $$0.12\ \mathrm{m}$$, spinning at $$1\ \mathrm{rad/s}. $$What is the required friction force to keep the object from sliding off?

Accepted Answer

$$0.24\ \mathrm{N}$$

Question 5

A 100 kg astronaut stands on a scale in a spaceship accelerating upward at $$10\ \mathrm{m/s^2$}. $$What does the scale read in kg?

Accepted Answer

$$200\ \mathrm{kg}$$

Question 6

A wheel starts from rest and accelerates at $$0.5\ \mathrm{$$rad/s^2$$}. $$What is the speed of a point on the edge of a $$0.10\ \mathrm{m}$$ radius disc after $$5\ \mathrm{s}$$?

Accepted Answer

$$0.50\ \mathrm{m/s}$$

Question 7

A 100 kg person is on an amusement park ride that drops with an acceleration of $$-5\ \mathrm{m/s^2$}. $$What does a scale under the person read in kg?

Accepted Answer

$$50\ \mathrm{kg}$$

Question 8

A bicyclist of mass $$100\ \mathrm{kg}$$ attempts to ride upside down through a loop of radius $$3\ \mathrm{m}. $$What is the minimum speed required at the top of the loop to maintain contact?

Accepted Answer

$$5.4\ \mathrm{m/s}$$

Question 9

A $$10\ \mathrm{kg}$$ block is at rest on a flat surface. A $$10\ \mathrm{N}$$ force is applied. If the static friction coefficient is $$0.5$$, what is the maximum static friction force?

Accepted Answer

$$49\ \mathrm{N}$$

Question 10

A $$100\ \mathrm{g}$$ mass is attached to a spring scale and raised at constant velocity. What force does the scale read?

Accepted Answer

$$0.98\ \mathrm{N}$$

Question 11

A rotating wheel has an initial angular velocity of $$+10\ \mathrm{rad/s}$$ and slows to $$+5\ \mathrm{rad/s} in$$ $$10\ \mathrm{s}$$ under constant angular acceleration. What is the angular acceleration?

Accepted Answer

$$-0.05\ \mathrm{$$rad/s^2$$}$$

Question 12

Which of the following best describes Newton's 3rd Law?

Accepted Answer

For every action, there is an equal and opposite reaction.

Question 13

A $$1\ \mathrm{kg}$$, $$2\ \mathrm{kg}$$, and $$3\ \mathrm{kg}$$ block are pushed together by a $$20\ \mathrm{N}$$ force on a frictionless surface. What is the acceleration of the system?

Accepted Answer

$$3.3\ \mathrm{m/s^2$}$$

Question 14

A block slides down an incline with friction. The coefficient of kinetic friction is $$\mu_k$$, the incline angle is $$	heta$$, and $$g is $$gravity. What is the acceleration?

Accepted Answer

$$g(\sin	heta - \mu_k\cos	heta)$$

Question 15

A $$10\ \mathrm{kg}$$ mass hangs from two ropes at $$45^\circ$$ angles. What is the tension in each rope?

Accepted Answer

$$69\ \mathrm{N}$$

Question 16

Which of the following statements is true regarding mass and weight?

Accepted Answer

Weight changes with gravity, mass does not.

Question 17

A $$1000\ \mathrm{kg}$$ car moves in a circle of radius $$100\ \mathrm{m} at$$ $$20\ \mathrm{m/s}. $$What is the required centripetal force?

Accepted Answer

$$4000\ \mathrm{N}$$

Question 18

A wheel starts at $$1\ \mathrm{rad/s}$$ and accelerates at $$2\ \mathrm{$$rad/s^2$$}. $$How many rotations does it make in $$2\ \mathrm{s}$$?

Accepted Answer

$$0.8$$ rotations

Question 19

Which of the following is true about objects at different radii on a rigid rotating disk?

Accepted Answer

They have the same angular speed.

Question 20

A $$100\ \mathrm{kg}$$ cyclist rides through a circular dip of radius $$5\ \mathrm{m} at$$ $$10\ \mathrm{m/s}. $$What is the normal force at the bottom of the dip?

Accepted Answer

$$3000\ \mathrm{N}$$

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