BIO Motion Camouflage in Dragonflies Dragonflies, whose ancestors were once the size of hawks, have prowled the skies in search of small flying insects for over 250 million years. Faster and more maneuverable than any other insect, they even fold their front two legs in flight and tuck them behind their head to be as streamlined as possible. They also employ an intriguing stalking strategy known as “motion camouflage” to approach their prey almost undetected. The basic idea of motion camouflage is for the dragonfly to move in such a way that the line of sight from the prey to the dragonfly is always in the same direction. Moving in this way, the dragonfly appears almost motionless to its prey, as if it were an object at infinity. Eventually the prey notices the dragonfly has grown in size and is therefore closer but by that time it’s too late for the prey to evade capture. A typical capture scenario is shown in Figure 3-51 , where the prey moves in the positive y direction with the constant speed u p = 0.750 m/s, and the dragonfly moves at an angle θ = 48.5° to the x axis with the constant speed v d . If the dragonfly chooses its speed correctly, the line of sight from the prey to the dragonfly will always be in the same direction—parallel to the x axis in this case. Figure 3-51 Problems 83, 84, 85, and 86 84. • Suppose the dragonfly now approaches its prey along a path with θ > 48.5°, but it still keeps the line of sight parallel to the x axis. IS the speed of the dragonfly in this new case greater than, less than, or equal to its speed in Problem 83?
BIO Motion Camouflage in Dragonflies Dragonflies, whose ancestors were once the size of hawks, have prowled the skies in search of small flying insects for over 250 million years. Faster and more maneuverable than any other insect, they even fold their front two legs in flight and tuck them behind their head to be as streamlined as possible. They also employ an intriguing stalking strategy known as “motion camouflage” to approach their prey almost undetected. The basic idea of motion camouflage is for the dragonfly to move in such a way that the line of sight from the prey to the dragonfly is always in the same direction. Moving in this way, the dragonfly appears almost motionless to its prey, as if it were an object at infinity. Eventually the prey notices the dragonfly has grown in size and is therefore closer but by that time it’s too late for the prey to evade capture. A typical capture scenario is shown in Figure 3-51 , where the prey moves in the positive y direction with the constant speed u p = 0.750 m/s, and the dragonfly moves at an angle θ = 48.5° to the x axis with the constant speed v d . If the dragonfly chooses its speed correctly, the line of sight from the prey to the dragonfly will always be in the same direction—parallel to the x axis in this case. Figure 3-51 Problems 83, 84, 85, and 86 84. • Suppose the dragonfly now approaches its prey along a path with θ > 48.5°, but it still keeps the line of sight parallel to the x axis. IS the speed of the dragonfly in this new case greater than, less than, or equal to its speed in Problem 83?
Dragonflies, whose ancestors were once the size of hawks, have prowled the skies in search of small flying insects for over 250 million years. Faster and more maneuverable than any other insect, they even fold their front two legs in flight and tuck them behind their head to be as streamlined as possible. They also employ an intriguing stalking strategy known as “motion camouflage” to approach their prey almost undetected.
The basic idea of motion camouflage is for the dragonfly to move in such a way that the line of sight from the prey to the dragonfly is always in the same direction. Moving in this way, the dragonfly appears almost motionless to its prey, as if it were an object at infinity. Eventually the prey notices the dragonfly has grown in size and is therefore closer but by that time it’s too late for the prey to evade capture.
A typical capture scenario is shown in Figure 3-51, where the prey moves in the positive y direction with the constant speed up = 0.750 m/s, and the dragonfly moves at an angle θ = 48.5° to the x axis with the constant speed vd. If the dragonfly chooses its speed correctly, the line of sight from the prey to the dragonfly will always be in the same direction—parallel to the x axis in this case.
Figure 3-51 Problems 83, 84, 85, and 86
84. • Suppose the dragonfly now approaches its prey along a path with θ > 48.5°, but it still keeps the line of sight parallel to the x axis. IS the speed of the dragonfly in this new case greater than, less than, or equal to its speed in Problem 83?
13.87 ... Interplanetary Navigation. The most efficient way
to send a spacecraft from the earth to another planet is by using a
Hohmann transfer orbit (Fig. P13.87). If the orbits of the departure
and destination planets are circular, the Hohmann transfer orbit is an
elliptical orbit whose perihelion and aphelion are tangent to the
orbits of the two planets. The rockets are fired briefly at the depar-
ture planet to put the spacecraft into the transfer orbit; the spacecraft
then coasts until it reaches the destination planet. The rockets are
then fired again to put the spacecraft into the same orbit about the
sun as the destination planet. (a) For a flight from earth to Mars, in
what direction must the rockets be fired at the earth and at Mars: in
the direction of motion, or opposite the direction of motion? What
about for a flight from Mars to the earth? (b) How long does a one-
way trip from the the earth to Mars take, between the firings of the
rockets? (c) To reach Mars from the…
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a cubic foot of argon at 20 degrees celsius is isentropically compressed from 1 atm to 425 KPa. What is the new temperature and density?
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