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Chapter 7: Q23Q (page 170)
How can a rocket change direction when it is far out in space and essentially in a vacuum?
When a rocket wants to change its direction, it ejects some gas opposite to the desired direction.
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The CM of an empty 1250-kg car is 2.40 m behind the front of the car. How far from the front of the car will the CM be when two people sit in the front seat 2.80 m from the front of the car, and three people sit in the back seat 3.90 m from the front? Assume that each person has a mass of 65.0 kg.
A 0.145-kg baseball pitched at 31.0 m/s is hit on a horizontal line drive straight back at the pitcher at 46.0 m/s. If the contact time between bat and ball is \({\bf{5}}{\bf{.00 \times 1}}{{\bf{0}}^{{\bf{ - 3}}}}\;{\bf{s}}\), calculate the force (assumed to be constant) between the ball and bat.
A bullet of mass \(m{\bf{ = 0}}{\bf{.0010}}\;{\bf{kg}}\) embeds itself in a wooden block with mass \(M{\bf{ = 0}}{\bf{.999}}\;{\bf{kg}}\), which then compresses a spring \(\left( {k{\bf{ = 140}}\;{\bf{N/m}}} \right)\) by a distance \(x{\bf{ = 0}}{\bf{.050}}\;{\bf{m}}\) before coming to rest. The coefficient of kinetic friction between the block and table is \(\mu {\bf{ = 0}}{\bf{.50}}\).
(a) What is the initial velocity (assumed horizontal) of the bullet?
(b) What fraction of the bullet's initial kinetic energy is dissipated (in damage to the wooden block, rising temperature, etc.) in the collision between the bullet and the block?
A wooden block is cut into two pieces, one with three times the mass of the other. A depression is made in both faces of the cut, so that a firecracker can be placed in it with the block reassembled. The reassembled block is set on a rough-surfaced table, and the fuse is lit. When the firecracker explodes inside, the two blocks separate and slide apart. What is the ratio of distances each block travels?
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