## Frictional Force in a Knee Joint| Further Applications of Newton’s Laws: Friction, Drag, and Elasticity| College Physics| Problem 5.3

(a) When rebuilding her car’s engine, a physics major must exert 300 N of force to insert a dry steel piston into a steel cylinder. What is the normal force between the piston and cylinder? (b) What force would she have to exert if the steel parts were oiled?

## Normal Force Between Steel Piston and Steel Cylinder| Further Applications of Newton’s Laws: Friction, Drag, and Elasticity| College Physics| Problem 5.2

(a) When rebuilding her car’s engine, a physics major must exert 300 N of force to insert a dry steel piston into a steel cylinder. What is the normal force between the piston and cylinder? (b) What force would she have to exert if the steel parts were oiled?

## Friction Force Between Steel and Teflon| Further Applications of Newton’s Laws: Friction, Drag, and Elasticity| College Physics| Problem 5.1

A physics major is cooking breakfast when he notices that the frictional force between his steel spatula and his Teflon frying pan is only 0.200 N. Knowing the coefficient of kinetic friction between the two materials, he quickly calculates the normal force. What is it?

## The force of a Powerful Motorcycle| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.10

A powerful motorcycle can produce an acceleration of 3.50m/s² while traveling at  90.0 km/h. At that speed the forces resisting motion, including friction and air resistance, total 400 N. (Air resistance is analogous to air friction. It always opposes the motion of an object.) What force does the motorcycle exert backward on the ground to produce its acceleration if the mass of the motorcycle with the rider is 245 kg?

## Two children pushing on a third child in a wagon| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.9

Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The first child exerts a force of 75.0 N, the second a force of 90.0 N, friction is 12.0 N, and the mass of the third child plus wagon is 23.0 kg. (a) What is the system of interest if the acceleration of the child in the wagon is to be calculated? (b) Draw a free-body diagram, including all forces acting on the system. (c) Calculate the acceleration. (d) What would the acceleration be if friction were 15.0 N?

## The deceleration that causes a blackout and temporary blindness| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.8

What deceleration of the rocket sled if it comes to rest in 1.1 s from a speed of 1000 km/h? (Such deceleration caused one test subject to black out and have temporary blindness.)

## The acceleration of One of Four rockets Burning| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.7

(a) If the rocket sled shown in Figure 4.32 starts with only one rocket burning, what is the magnitude of its acceleration? Assume that the mass of the system is 2100 kg, the thrust T is 24,000 N, and the force of friction opposing the motion is known to be 650 N. (b) Why is the acceleration not one-fourth of what it is with all rockets burning?

## Deceleration of a Rocket Sled| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.6

The same rocket sled drawn in Figure 4.31 is decelerated at a rate of 196 m/s². What force is necessary to produce this deceleration? Assume that the rockets are off. The mass of the system is 2100 kg.

## Force Exerted by a Lawnmower| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.5

The net external force on the 24-kg mower is stated to be 51 N. If the force of friction opposing the motion is 24 N, what force F (in newtons) is the person exerting on the mower? Suppose the mower is moving at 1.5 m/s when the force F is removed. How far will the mower go before stopping?

## Measuring the mass of an Austronaut| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.4

Since astronauts in orbit are apparently weightless, a clever method of measuring their masses is needed to monitor their mass gains or losses to adjust diets. One way to do this is to exert a known force on an astronaut and measure the acceleration produced. Suppose a net external force of 50.0 N is exerted and the astronaut’s acceleration is measured to be 0.893 m/s²  (a) Calculate her mass. (b) By exerting a force on the astronaut, the vehicle in which they orbit experiences an equal and opposite force. Discuss how this would affect the measurement of the astronaut’s acceleration. Propose a method in which the recoil of the vehicle is avoided.