A 2.0-kg block slides down a fixed, rough curved track. The block has a speed of 5.0 m/s after its height above a horizontal surface has decreased by 1.8 m. Assume the block starts from rest. What is the change in mechanical energy of the block caused by the force of friction during this descent?
A. ?14 J
B. ?12 J
C. ?10 J
D. ?16 J
E. ?25 J
Answer: C
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A 30-kg child rides on a circus Ferris wheel that takes her around a vertical circular path with a radius of 20 m every 22 s. What is the magnitude of the resultant force on the child at the highest point on this trajectory?
A. 49 N B. 0.29 kN C. 0.34 kN D. 0.25 kN E. 0.76 kN
Because we know that the half-lives of many radioactive isotopes are millions of years, we can deduce that
a. the longer it exists the more radioactive nuclei Earth produces. b. the sun is the source of all the radioactive nuclei on Earth. c. there must have been many more radioactive nuclei on Earth when life began. d. there must have been far fewer radioactive nuclei on Earth before life began. e. the natural radioactivity of minerals on the Earth was created by the Earth's internal temperature.
The__________is the period of time after the glow of the big bang faded into the infrared and before the birth of the first stars, during which the Universe expanded in darkness
A) space age B) dark age C) atomic age D) ice age