Radiation Activity: A certain substance has a half-life of 5.0 hours. How many nuclei of the substance are required to give an initial activity of 6.0 ?Ci? (1 Ci = 3.7 × 1010 Bq)
A. 5.8 × 109 nuclei
B. 8.5 × 108 nuclei
C. 6.3 × 108 nuclei
D. 3.2 × 109 nuclei
E. 2.4 × 109 nuclei
Answer: A
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Two masses are connected by a string which passes over a pulley with negligible mass and friction. One mass hangs vertically and one mass slides on a 30.0 degrees frictionless incline. The vertically hanging mass is 4.0 kg and the mass on the incline is 6.00 kg. The acceleration of the 4.00 kg mass is
A. 0.980 
B. 3.92
C. 5.75
D. 6.86
E. 7.84
Bumpers on cars are not of much use in a collision. To see why, calculate the average force a bumper would have to exert
if it brought a 1200-kg car (a so-called compact model) to a rest in 15 cm when the car had an initial speed of 2.0 m/s (about 4.5 mph). (Bumpers are built with springs that compress to provide a stopping force without, hopefully, denting the metal.) A) 1.8 × 104 N B) 1.6 × 104 N C) 5.4 × 104 N D) 6.5 × 105 N E) 3.2 × 104 N
What type of graph was obtained in Procedure 1, Step 6?
Uranus was discovered by accident, and mistaken for a comet at first
Indicate whether the statement is true or false