A truck, initially at rest, rolls down a frictionless hill and attains a speed of 20 m/s at the bottom. To achieve a speed of 40 m/s at the bottom, how many times higher must the hill be?
A. half the height
B. the same height
C. 12 times the height
D. twice the height
E. four times the height
E. four times the height
If the speed has doubled, then the kinetic energy is 4X as much. Therefore the initial potential energy must be 4X as much.
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Why is iron significant to understanding how a supernova occurs?
A) Iron is the heaviest of all atomic nuclei, and thus no heavier elements can be made. B) Supernovae often leave behind neutron stars, which are made mostly of iron. C) The fusion of iron into uranium is the reaction that drives a supernova explosion. D) Iron cannot release energy either by fission or fusion.
The average intensity of the sunlight in Miami, Florida, is 1.04 kW/m2
For surfaces on which the light is all absorbed, what is the average value of the radiation pressure due to this sunlight in Miami? (c = 3.00 × 108 m/s, ?0 = 4? × 10-7 T ? m/A, ?0 = 8.85 × 10-12 C2/N ? m2) A) 2.28 µPa B) 1.73 µPa C) 6.93 µPa D) 3.47 µPa E) 9.78 µPa
A person with normal eyesight uses a converging lens of focal length 10 cm. He holds the lens close to his eye to finish an engraving job. At what distance from the job he must hold the lens?
A) -7.1 cm B) 7.1 cm C) -30 cm D) 30 cm E) 20 cm
The activity of a sample reduces from 7.55 × 109 Bq to 5.11 × 109 Bq in 5.50 months
(a) What is the half life? (b) How many months must one wait for the activity to decrease to 10%?