1. How much kinetic energy did 93.9-kg Usain Bolt have when he broke the Olympic
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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
Pretty straight forward, since you are given all of the variables you need for rach question. Just plug the numbers in to the appropriate equation below.
Kinetic Energy Due to Motion: KE = mv2/2
where m is mass, v is velocity
Potential Energy Due to Gravity: PE = mgh
where m is mass, g is acceleration of gravity (9.81m/s2), and h is the height above the origin
Potential Energy Due to a Spring: PE = kx2/2
where k is the spring constant (in N/m), and x is the distance the string is streched/compressed from equilibrium
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