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Physics For Scientists & Engineers
Found in: Page 138
Physics For Scientists & Engineers

Physics For Scientists & Engineers

Book edition 9th Edition
Author(s) Raymond A. Serway, John W. Jewett
Pages 1624 pages
ISBN 9781133947271

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Short Answer

A car is moving forward slowly and is spending up. A student claims that “the car’s engine exerts a force on itself” or that “the car’s engine exerts a force on the car.”

(a) Argue that this idea cannot be accurate and that friction exerted by the road is the propulsive force on the car. Make your evidence and reasoning as persuasive as possible.

(b) Is it static or kinetic friction?

Suggestion: Consider light gravel. Consider a sharp print of the tire tread on an asphalt road, obtained by coating the thread with dust.

If a car is stuck in on an icy road, with its wheel spinning wildly, you know the car has great difficulty moving forward until it catches on a rough patch.

See the step by step solution

Step by Step Solution

TABLE OF CONTENTS :
TABLE OF CONTENTS

Step1: A concept:

Friction is the force that prevents the tire rubber from sliding on the road surface. However, things are not really that simple. Consider two different frictions; static and kinetic friction. Static Friction - the force of friction between surfaces that are not moving relative to each other.

Step 2: (a) The road's friction propels you forward:

The force that causes the car to speed ahead is friction from the road. Burning gasoline can provide energy for the motion, but only external forces- forces exerted by objects outside can accelerate the car.

Step 3: (b) It is a case of static friction:

If the car moves forward slowly as it speeds up, then its tires do not slip on the surface.

The rubber contacting the road moves towards the rear of the car, and static friction opposes relative sliding motion by exerting a force on the rubber towards the front of the car.

If the car is under control, the relative speed is zero along the lines where the rubber meets the road, and static friction acts rather than kinetic friction.

Most popular questions for Physics Textbooks

As shown in figure CQ5.22, student A, a 55 kg girl, sits on one chair with metal runners, at rest on a classroom floor. Student B, an 80 kg boy, sits on an identical chair. Both students keep their feet off the floor. A rope runs from student A’s hands around a light pulley and then over her shoulder to the hands of a teacher standing on the floor behind her. The low-friction axle of the pulley is attached to a second rope held by student B, all ropes run parallel to the chair runners.

  1. If student A pulls on her end of the rope, will her chair or will B’s chair slide on the floor? Explain why?
  2. If instead, the teacher pulls on his rope end, which chair slides? Why this one?
  3. If student B pulls on his rope, which chair slides? Why?
  4. Now the teacher ties his end of the rope to student A’s chair. Student A pulls on the end of the rope in her hands. Which chair slides and why?

Give reasons for the answers to each of the following questions:

(a)Can a normal force be horizontal?

(b) Can a normal force be directed vertically downward?

(c) Consider a tennis ball in contact with a stationary floor and with nothing else. Can the normal force be different in magnitude from the gravitational force exerted on the ball?

(d) Can the force exerted by the floor on the ball be different in magnitude from the force the ball exerts on the floor?

Question: Objects with masses m1=10.0 kg and m2=5.0 kg are connected by a light string that passes over a frictionless pulley as in Figure P5.40. If, when the system starts from rest, m2falls 1.00 m in 1.20 s, determine the coefficient of kinetic friction between m1and the table.

Balancing carefully, three boys inch out onto a horizontal tree branch above a pond, each planning to dive in separately. The third boy in line notices that the branch is barley strong enough to support them. He decides to jump straight up and land back on the branch to break it, spilling all three into the pond. When does he start to carry out his plan, at which precise moment does the branch break? Explain. Suggestion: Pretend to be the third boy and imitate what he does in slow motion. If slow motion. If you are still ensure, stand on a bathroom scale and repeat the suggestion.

Question: A block of mass 2.20 kg is accelerated across a rough surface by a light cord passing over a small pulley as shown in Figure P5.99. The tension T in the cord is maintained at 10.0 N, and the pulley is 0.100 m above the top of the block. The coefficient of kinetic friction is 0.400. (a) Determine the acceleration of the block when x = 0.400 m. (b) Describe the general behavior of the acceleration as the block slides from a location where x is large to x = 0 . (c) Find the maximum value of the acceleration and the position x for which it occurs. (d) Find the value of x for which the acceleration is zero.
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