# a 4 - 5 Comic-strip hero Superman meets an asteroid in...

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PHYSICS 309K, FALL 2004 HOMEWORK 4, Due Monday 10/04/04 1. A car with a mass of 100 kg moves at 20 m/s. What braking force is needed to bring the car to a halt in 10 s? 2. Lillian (mass 40.0 kg) standing on slippery ice catches her leaping dog (mass 15 kg) moving horizontally at 3.0 m/s. What is the speed of Lillian and her dog after the catch? 3. A 2-kg ball of putty moving to the right has a head-on inelastic collision with a 1-kg putty ball moving to the left. If the combined blob doesn’t move just after collision, what can you conclude about the relative speeds of the balls before they collided? 4. A 5-kg ﬁsh swimming 1 m/s swallows an absent minded 1-kg ﬁsh swimming toward it at a velocity that brings both ﬁsh to a halt immediately after lunch. What is the velocity V of the smaller ﬁsh before lunch?
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Unformatted text preview: 5. Comic-strip hero Superman meets an asteroid in outer space, and hurls it at 800 m/s, as fast as a bullet. The asteroid is a thousand times more massive than Superman. In the strip, Superman is seen at rest after the throw. Taking physics into account, what would be his recoilvelocity? 6. Two automobiles, each of mass 100 kg, are moving at the same speed, 20 m/s, when they collide and stick together. In what direction and at what speed does the wreckage move (a) if one car was driving north and one south? (b) if one car was driving north and one east? 7. Can you run fast enough to have the same momentum as an automobile rolling at 1 mi/h? Assume the mass of the automobile to be between 1000 kg and 2000 kg....
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