1. How much kinetic energy did 93.9-kg Usain Bolt have when he broke the Olympic

Question

1. How much kinetic energy did 93.9-kg Usain Bolt have when he broke the Olympic 100-m dash record with a speed of 10.25 m/s?





2. A 70.0 kg stuntman is attached to a bungee cord. He is standing on a ledge that is 50 m high. How much gravitational potential energy does he have?





3. The stuntman jumps off the ledge and bobs up and down for a while. When he finally stops, the cord is stretched 29 m. If the spring constant of the bungee cord is 71.8 N/m, how much elastic potential energy does the stuntman have?





4. How much gravitational potential energy did King Kong have at the top of the Empire State Building? King Kong had a mass of 25×106 kg. The Empire State Building is 381 m (1,250 feet) tall.





5. A rifle can fire a 4.20-gram bullet at a speed of 965 m/s. Calculate the kinetic energy of the bullet after leaves the barrel of the rifle.





6. In 1992, David Engwall of California used a slingshot to launch at 62 g dart. The dart traveled a distance of 477 m (almost 5 football fields). The amount of potential energy in the slingshot was 140 J. If the spring constant of the slingshot is 30000 N/m, how far was the slingshot stretched?














6. Naim Suleimanoglu of Turkey has a mass of 62 kg (136 lbs), yet he can lift 3 times his mass. This feat has earned him the nickname “Pocket Hercules”. How much potential energy would a barbell have if he lifted the barbell 1.7 m above the floor?





7. Susie Maroney from Australia set a women’s record in long-distance swimming by swimming 93.625 km in 24 h.

(a) What her average speed in m/s?





(b) If she had a mass of 55 kg, how much kinetic energy did she have?





8. A 7.85×1011 kg comet strikes the Earth at a speed of 25 km/s. Which is greater, the amount of kinetic energy this comet had or the amount of energy released by the largest nuclear weapon ever built (4.2×1015 J = 100 million tons of TNT)? Such a comet collision has been suggested as having caused the extinction of the dinosaurs.

Explanation / Answer

1.) KE= .5 mv2 =.5 * 93.9 * 10.252 =4932.6 J 2.)PE= mgh= 70 * 9.8 * 50 = 34300 J 3.)elastic potential energy = .5 kx2 = .5 * 71.8 * 292 = 30191.9 J 4.)PE= mgh =25 *106 * 9.8 * 381 =9894570 J =9894.57 KJ 5.)KE= .5 mv2 = .5 * 4.20 * 10-3 * 9652 =1955.572 J 6.) (1) Here PE of slingshot converted to KE .5 kx2 = .5 * 30000 * x2 = 140 x2 = 140 /(.5 * 30000) =.009333 x = .0966 m 6.) (2) mass of barbell= 62 * 3 =186 Kg PE = mgh = 186 * 9.8 * 1.7 =3098.76 J 7.) (a) average speed = total distance / total time average speed = (93.625 * 1000) / (24 * 60 * 60) average speed = 93625 / 86400 = 1.08 m/s (b) KE = .5 mv2 = .5 * 55 * 1.082 = 32.076 J 8.)KE = .5 mv2 = .5 * 7.85×1011 * 250002 = 2480.1 * 106 KJ This is greater than 4.2×1015 J

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