Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 4: Problem 7

Which of the following observations about the friction force is (are) incorrect? a) The magnitude of the kinetic friction force is always proportional to the normal force b) The magnitude of the static friction force is always proportional to the normal force. c) The magnitude of the static friction force is always proportional to the external applied force. d) The direction of the kinetic friction force is always opposite the direction of the relative motion of the object writh respect to the surface the object moves on. e) The direction of the static friction force is always opposite that of the impending motion of the object relative to the surface it rests on f) All of the above are correct.

Short Answer

Expert verified
Answer: C) Static friction force proportionality with external applied force and F) All statements are correct.

Step by step solution

01

A) Kinetic friction force proportionality with normal force.

This statement is true. Kinetic friction force (\(f_k\)) is always proportional to the normal force (\(N\)). The proportionality constant is the coefficient of kinetic friction (\(\mu_k\)). So mathematically, it can be written as \(f_k = \mu_k N\).
02

B) Static friction force proportionality with normal force.

This statement is also true. The maximum static friction force (\(f_{s,max}\)) is proportional to the normal force (\(N\)). The proportionality constant is the coefficient of static friction (\(\mu_s\)). Mathematically, it can be written as \(f_{s,max} = \mu_s N\). However, it's important to note that the actual static friction force can vary from 0 to the maximum value.
03

C) Static friction force proportionality with external applied force.

This statement is incorrect. The static friction force is not always proportional to the external applied force. For a given normal force, the static friction force will adjust to balance the applied force up to a maximum value of the static friction force (\(f_{s,max} = \mu_s N\)). Beyond that, the object may start moving due to an external force that exceeds the static friction force.
04

D) Kinetic friction force direction.

This statement is true. The kinetic friction force always acts in the opposite direction of the relative motion of the object with respect to the surface the object is moving on.
05

E) Static friction force direction.

This statement is true. The static friction force always acts in the opposite direction of the impending motion of the object relative to the surface it rests on.
06

F) All statements are correct.

This statement is incorrect. As we have analyzed, statement C is incorrect. Therefore, all the statements are not correct. In conclusion, the incorrect observations about friction force are C) and F).

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

4.32 A hanging mass, \(M_{1}=0.50 \mathrm{~kg}\), is attached by a light string that runs over a frictionless pulley to a mass \(M_{2}=1.50 \mathrm{~kg}\) that is initially at rest on a frictionless table. Find the magnitude of the acceleration, \(a,\) of \(M_{2}\)

You are at the shoe store to buy a pair of basketball shoes that have the greatest traction on a specific type of hardwood. To determine the coefficient of static friction. \(\mu\), you place each shoe on a plank of the wood and tilt the plank to an angle \(\theta\), at which the shoe just starts to slide. Obtain an expression for \(\mu\) as a function of \(\theta\).

A tractor pulls a sled of mass \(M=1000\). kg across level ground. The coefficient of kinetic friction between the sled and the ground is \(\mu_{k}=0.600 .\) The tractor pulls the sled by a rope that connects to the sled at an angle of \(\theta=30.0^{\circ}\) above the horizontal. What magnitude of tension in the rope is necessary to move the sled horizontally with an acceleration \(a=2.00 \mathrm{~m} / \mathrm{s}^{2} ?\)

A hanging mass, \(M_{1}=0.400 \mathrm{~kg}\), is attached by a light string that runs over a frictionless pulley to a mass \(M_{2}=1.20 \mathrm{~kg}\) that is initially at rest on a frictionless ramp. The ramp is at an angle of \(\theta=30.0^{\circ}\) above the horizontal, and the pulley is at the top of the ramp. Find the magnitude and direction of the acceleration, \(a_{2}\), of \(M_{2}\).

4.71 A block of mass \(20.0 \mathrm{~kg}\) supported by a vertical massless cable is initially at rest. The block is then pulled upward with a constant acceleration of \(2.32 \mathrm{~m} / \mathrm{s}^{2}\). a) What is the tension in the cable? b) What is the net force acting on the mass? c) What is the speed of the block after it has traveled \(2.00 \mathrm{m?}\)
See all solutions

Recommended explanations on Physics Textbooks

Measurements

Read Explanation

Physical Quantities And Units

Read Explanation

Engineering Physics

Read Explanation

Astrophysics

Read Explanation

Work Energy and Power

Read Explanation

Torque and Rotational Motion

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free