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Chapter 4: Q4CQ (page 159)
What is the relationship between weight and mass? Which is an intrinsic, unchanging property of a body?
Weight is the product of mass and force due to gravity. Mass is an intrinsic, unchanging property of the body.
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If the acceleration of a system is zero, are no external forces acting on it? What about internal forces? Explain your answers.
What is the ratio of the strength of the strong nuclear force to that of the electromagnetic force? Based on this ratio, you might expect that the strong force dominates the nucleus, which is true for small nuclei. Large nuclei, however, have sizes greater than the range of the strong nuclear force. At these sizes, the electromagnetic force begins to affect nuclear stability. These facts will be used to explain nuclear fusion and fission later in this text.
A brave but inadequate rugby player is being pushed backward by an opposing player who is exerting a force of 800 N on him. The mass of the losing player plus equipment is 90.0 kg, and he is accelerating at 1.20 m/s2 backward. (a) What is the force of friction between the losing player’s feet and the grass? (b) What force does the winning player exert on the ground to move forward if his mass plus equipment is 110 kg?
(c) Draw a sketch of the situation showing the system of interest used to solve each part. For this situation, draw a free-body diagram and write the net force equation.
A freight train consists of two 8.00×104 -kg engines and 45 cars with average masses of 5.50×104 kg.
(a) What force must each engine exert backward on the track to accelerate the train at a rate of 5.00×10–2 m/s2 if the force of friction is 7.50×105 N, assuming the engines exert identical forces? This is not a large frictional force for such a massive system. Rolling friction for trains is small, and consequently trains are very energy-efficient transportation systems.
(b) What is the force in the coupling between the 37th and 38th cars (this is the force each exerts on the other), assuming all cars have the same mass and that friction is evenly distributed among all of the cars and engines?
Integrated Concepts When starting a foot race, a 70.0-kg sprinter exerts an average force of 650 N backward on the ground for 0.800 s.
(a) What is his final speed?
(b) How far does he travel?
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