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A 68.5-kg skater moving initially at 2.40 m/s on rough horizontal ice comes to rest uniformly in 3.52 s due to friction from the ice. What force does friction exert on the skater?

Short Answer

Expert verified
The friction force is approximately -46.7 N, acting opposite to the motion.

Step by step solution

01

Understand the Problem

We are given the mass of a skater, the initial velocity, the final velocity, and the time taken to come to rest. The objective is to find the force of friction exerted on the skater, which will require using principles of mechanics like velocity, acceleration, and force.
02

Identify Known Values

The known values are the initial velocity of the skater \(v_i = 2.40 \text{ m/s}\), the final velocity \(v_f = 0 \text{ m/s}\), the time taken \(t = 3.52 \text{ s}\), and the mass of the skater \(m = 68.5 \text{ kg}\).
03

Find Deceleration

Since the skater comes to a rest uniformly, we use the equation of motion: \(v_f = v_i + at\). Substitute \(v_f = 0\), \(v_i = 2.40 \text{ m/s} \), and \(t = 3.52 \text{ s} \) to solve for acceleration \(a\). \(0 = 2.40 + a \times 3.52\), thus \(a = -\frac{2.40}{3.52}\approx -0.682\) m/s².
04

Apply Newton's Second Law

Using Newton's Second Law \( F = ma \), substitute \(m = 68.5 \text{ kg} \) and \(a = -0.682 \text{ m/s}^2\). Therefore, \( F = 68.5 \times (-0.682) \approx -46.7 \text{ N} \). The negative sign indicates that the force is acting opposite to the motion.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Newton's Second Law
Newton's Second Law of Motion is a fundamental principle in physics that relates the force applied to an object to its mass and the acceleration it experiences. The law is often expressed with the famous formula:
  • \( F = ma \)
where:
  • \( F \) is the net force applied to the object, measured in Newtons (N)
  • \( m \) is the mass of the object in kilograms (kg)
  • \( a \) is the acceleration in meters per second squared (\( \text{m/s}^2 \))
In the context of the exercise, the force exerted by friction acts against the skater's motion, causing them to slow down and eventually stop. This deceleration is due to the negative acceleration resulting from the force of friction. By measuring the skater’s mass and the acceleration, we can determine the amount of force required to bring the skater to a stop over a given period.
Exploring Deceleration
Deceleration is simply negative acceleration, meaning it is the process of slowing down. It's quantified with the same units as acceleration, \( \text{m/s}^2 \), but it acts in the direction opposite to the motion.When calculating deceleration, we use the formula:
  • \( a = \frac{v_f - v_i}{t} \)
where:
  • \( v_f \) is the final velocity
  • \( v_i \) is the initial velocity
  • \( t \) is the time interval over which the change occurs
In the exercise example, the skater is initially moving at 2.40 m/s and comes to rest, so the final velocity is 0. By inserting these values into the deceleration formula, we understand how quickly they slow down. The deceleration value is crucial for determining how strong the frictional force needs to be to stop the skater within the specified time.
Understanding Uniform Motion
Uniform motion refers to motion at a constant speed in a straight line. It's characterized by having both a constant velocity and zero acceleration. In our case, the skater starts in uniform motion, gliding smoothly over the ice until the frictional force comes into play, causing deceleration. If there were no friction, and thus no external forces acting on the skater, they would continue in uniform motion indefinitely according to Newton's First Law of Motion (law of inertia). However, because friction acts in the opposite direction, it breaks this uniform motion. It causes the skater to experience a uniform deceleration, bringing them to a stop. This transition from uniform motion to resting illustrates how external forces and uniform motion concepts work together in practical situations.

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Most popular questions from this chapter

An 8.00-kg box sits on a level floor. You give the box a sharp push and find that it travels 8.22 m in 2.8 s before coming to rest again. (a) You measure that with a different push the box traveled 4.20 m in 2.0 s. Do you think the box has a constant acceleration as it slows down? Explain your reasoning. (b) You add books to the box to increase its mass. Repeating the experiment, you give the box a push and measure how long it takes the box to come to rest and how far the box travels. The results, including the initial experiment with no added mass, are given in the table: In each case, did your push give the box the same initial speed? What is the ratio between the greatest initial speed and the smallest initial speed for these four cases? (c) Is the average horizontal force \(f\) exerted on the box by the floor the same in each case? Graph the magnitude of force \(f\) versus the total mass \(m\) of the box plus its contents, and use your graph to determine an equation for \(f\) as a function of \(m\).

A small car of mass 380 kg is pushing a large truck of mass 900 kg due east on a level road. The car exerts a horizontal force of 1600 N on the truck. What is the magnitude of the force that the truck exerts on the car?

(a) An ordinary flea has a mass of 210 \(\mu\)g. How many newtons does it weigh? (b) The mass of a typical froghopper is 12.3 mg. How many newtons does it weigh? (c) A house cat typically weighs 45 N. How many pounds does it weigh, and what is its mass in kilograms?

A 75.0-kg man steps off a platform 3.10 m above the ground. He keeps his legs straight as he falls, but his knees begin to bend at the moment his feet touch the ground; treated as a particle, he moves an additional 0.60 m before coming to rest. (a) What is his speed at the instant his feet touch the ground? (b) If we treat the man as a particle, what is his acceleration (magnitude and direction) as he slows down, if the acceleration is assumed to be constant? (c) Draw his freebody diagram. In terms of the forces on the diagram, what is the net force on him? Use Newton's laws and the results of part (b) to calculate the average force his feet exert on the ground while he slows down. Express this force both in newtons and as a multiple of his weight.

A mysterious rocket-propelled object of mass 45.0 kg is initially at rest in the middle of the horizontal, frictionless surface of an ice-covered lake. Then a force directed east and with magnitude \(F(t) =\) (16.8 N/s)\(t\) is applied. How far does the object travel in the first 5.00 s after the force is applied?

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