Chapter 8: Problem 16
Can the center of mass of an object be located at a point outside the object, that is, at a point in space where no part of the object is located? Explain.
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Chapter 8: Problem 16
Can the center of mass of an object be located at a point outside the object, that is, at a point in space where no part of the object is located? Explain.
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A 350 -kg cannon, sliding freely on a frictionless horizontal plane at a speed of \(7.5 \mathrm{~m} / \mathrm{s}\), shoots a 15 -kg cannonball at an angle of \(55^{\circ}\) above the horizontal. The velocity of the ball relative to the cannon is such that when the shot occurs, the cannon stops cold. What is the velocity of the ball relative to the cannon?
One important characteristic of rocket engines is the specific impulse, which is defined as the total impulse (time integral of the thrust) per unit ground weight of fuel/oxidizer expended. (The use of weight, instead of mass, in this definition is due to purely historical reasons.) a) Consider a rocket engine operating in free space with an exhaust nozzle speed of \(v\). Calculate the specific impulse of this engine. b) A model rocket engine has a typical exhaust speed of \(v_{\text {toy }}=800 . \mathrm{m} / \mathrm{s}\). The best chemical rocket engines have exhaust speeds of approximately \(v_{\text {chem }}=4.00 \mathrm{~km} / \mathrm{s} .\) Evaluate and compare the specific impulse values for these engines.
A man with a mass of 55 kg stands up in a \(65-\mathrm{kg}\) canoe of length \(4.0 \mathrm{~m}\) floating on water. He walks from a point \(0.75 \mathrm{~m}\) from the back of the canoe to a point 0.75 m from the front of the canoe. Assume negligible friction between the canoe and the water. How far does the canoe move?
Find the center of mass of a rectangular plate of length \(20.0 \mathrm{~cm}\) and width \(10.0 \mathrm{~cm} .\) The mass density varies linearly along the length. At one end, it is \(5.00 \mathrm{~g} / \mathrm{cm}^{2}\); at the other end, it is \(20.0 \mathrm{~g} / \mathrm{cm}^{2}\)
A spacecraft engine creates \(53.2 \mathrm{MN}\) of thrust with a propellant velocity of \(4.78 \mathrm{~km} / \mathrm{s}\). a) Find the rate \((d m / d t)\) at which the propellant is expelled. b) If the initial mass is \(2.12 \cdot 10^{6} \mathrm{~kg}\) and the final mass is \(7.04 \cdot 10^{4} \mathrm{~kg},\) find the final speed of the spacecraft (assume the initial speed is zero and any gravitational fields are small enough to be ignored). c) Find the average acceleration till burnout (the time at which the propellant is used up; assume the mass flow rate is constant until that time).
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