![]() ![]() Well, Admiral, it's probably the best course, but let me talk to the CNO before I make a final decision. I must pay special thanks to Jared Kieling, an editor of consummate skill, who detoured me away from many false paths as we explored the Titanic together. John Chase and William Felix for data on gold value and bullion shipments. And now he's off in Nova Scotia, living among the stunted trees and frost heaves, where nobody - not even short - memoried editors - can reach him easily. Does it seem high enough to cause damage even though it is lower than the force with no glove?ħ: Using energy considerations, calculate the average force a 60.0-kg sprinter exerts backward on the track to accelerate from 2.00 to 8.00 m/s in a distance of 25.0 m, if he encounters a headwind that exerts an average force of 30.0 N against him.Truth to tell, I don't remember if he sent in a manuscript through the mail first, or telephoned for an appointment to visit the office. (c) Discuss the magnitude of the force with glove on. (b) Calculate the force exerted by an identical blow in the gory old days when no gloves were used and the knuckles and face would compress only 2.00 cm. (a) Calculate the force exerted by a boxing glove on an opponent’s face, if the glove and face compress 7.50 cm during a blow in which the 7.00-kg arm and glove are brought to rest from an initial speed of 10.0 m/s. Calculate the magnitude of the average force on a bumper that collapses 0.200 m while bringing a 900-kg car to rest from an initial speed of 1.1 m/s.Ħ: Boxing gloves are padded to lessen the force of a blow. The bumper cushions the shock by absorbing the force over a distance. Calculate the force exerted on the car and compare it with the force found in part (a).ĥ: A car’s bumper is designed to withstand a 4.0-km/h (1.1-m/s) collision with an immovable object without damage to the body of the car. #WORKDONE UNDER GRAPH FULL#(b) Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. You will need to look up the definition of a nautical mile (1 knot = 1 nautical mile/h).Ĥ: (a) Calculate the force needed to bring a 950-kg car to rest from a speed of 90.0 km/h in a distance of 120 m (a fairly typical distance for a non-panic stop). Why?ġ: Compare the kinetic energy of a 20,000-kg truck moving at 110 km/h with that of an 80.0-kg astronaut in orbit moving at 27,500 km/h.Ģ: (a) How fast must a 3000-kg elephant move to have the same kinetic energy as a 65.0-kg sprinter running at 10.0 m/s? (b) Discuss how the larger energies needed for the movement of larger animals would relate to metabolic rates.ģ: Confirm the value given for the kinetic energy of an aircraft carrier in Chapter 7.6 Table 1. Net work is defined to be the sum of work done by all external forces-that is, net work is the work done by the net external force\textbf.ģ: When solving for speed in Example 3, we kept only the positive root. Let us start by considering the total, or net, work done on a system. We will see in this section that work done by the net force gives a system energy of motion, and in the process we will also find an expression for the energy of motion. We know from the study of Newton’s laws in Chapter 4 Dynamics: Force and Newton’s Laws of Motion that net force causes acceleration. We will also develop definitions of important forms of energy, such as the energy of motion. We will find that some types of work leave the energy of a system constant, for example, whereas others change the system in some way, such as making it move. In this section we begin the study of various types of work and forms of energy. ![]() Some of the energy imparted to the stone blocks in lifting them during construction of the pyramids remains in the stone-Earth system and has the potential to do work. In fact, the building of the pyramids in ancient Egypt is an example of storing energy in a system by doing work on the system. In contrast, work done on the briefcase by the person carrying it up stairs in Chapter 7.1 Figure 1(d) is stored in the briefcase-Earth system and can be recovered at any time, as shown in Chapter 7.1 Figure 1(e). For example, if the lawn mower in Chapter 7.1 Figure 1(a) is pushed just hard enough to keep it going at a constant speed, then energy put into the mower by the person is removed continuously by friction, and eventually leaves the system in the form of heat transfer. What happens to the work done on a system? Energy is transferred into the system, but in what form? Does it remain in the system or move on? The answers depend on the situation.
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