A gold thief is robbing a bullion exchange and is cornered by the police. He climbs to the top of the building which is 500 ft above the street. To keep from being caught with the goods, he drops his sack of loot which weighs 32 lbs. Calculate the total energy of the loot at the instant of free fall. Calculate the total energy of the loot after 4s of free fall and prove that energy is conserved.
Solution:
Total energy at the top = mgh
=> E = 32 x 32.1 x 500
=> E =513600 lbft^2s^2
After 4 s
Speed v = g x t
=> v = 32.1 x 4 = 128.4 ft/s
Heigt covered = 0.5 g t^2 = 0.5 x 32.1 x 4 x4
=> height = 256.8 ft
Energy = 0.5mv^2 + mgh
=> Energy = 0.5 x 32 x 128.4^2 + 32 x 32.1 x(500 - 256.8)
=> energy = 513600
Hence the energy is conserved
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A gold thief is robbing a bullion exchange and is cornered by the police. He climbs...