Chapter 7: Q24Q (page 170)
Bob and Jim decide to play tug-of-war on a frictionless (icy) surface. Jim is considerably stronger than Bob, but Bob weighs 160 lb whereas Jim weighs 145 lb. Who loses by crossing over the midline first? Explain.
Jimi crosses the midline first and loses.
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A novice pool player is faced with the corner pocket shot shown in Fig. 7–49. Relative dimensions are also shown. Should the player worry that this might be a “scratch shot,” in which the cue ball will also fall into a pocket? Give details. Assume equal-mass balls and an elastic collision. Ignore spin.
A (lightweight) pallet has a load of ten identical cases of tomato paste (see Fig. 7–39), each of which is a cube of length \(l\). Find the center of gravity in the horizontal plane, so that the crane operator can pick up the load without tipping it.
FIGURE 7-39
Problem 53.
A 95-kg fullback is running at \({\bf{3}}{\bf{.0}}\;{{\bf{m}} \mathord{\left/{\vphantom {{\bf{m}} {\bf{s}}}} \right.\\} {\bf{s}}}\) to the east and is stopped in 0.85 s by a head-on tackle by a tackler running due west. Calculate
(a) the original momentum of the fullback,
(b) the impulse exerted on the fullback,
(c) the impulse exerted on the tackler, and
(d) the average force exerted on the tackler.
A 725-kg two-stage rocket is traveling at a speed of \({\bf{6}}{\bf{.60 \times 1}}{{\bf{0}}^{\bf{3}}}\;{\bf{m/s}}\) away from Earth when a predesigned explosion separates the rocket into two sections of equal mass that then move with a speed of \({\bf{2}}{\bf{.80 \times 1}}{{\bf{0}}^{\bf{3}}}\;{\bf{m/s}}\)relative to each other along the original line of motion.
(a) What is the speed and direction of each section (relative to Earth) after the explosion?
(b) How much energy was supplied by the explosion? [Hint: What is the change in kinetic energy as a result of the explosion?]
(II) Calculate the force exerted on a rocket when the propelling gases are being expelled at a rate of 1300 kg/s with a speed of \(4.5 \times {10^4}\;{\rm{m/s}}\).
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