A 0.20-km wide river has a uniform flow speed of 3.0 m/s toward the east. A boat with a speed of 8.0 m/s relative to the water leaves the south bank and heads in such a way that it crosses to a point directly north of its departure point. How long does it take the boat to cross the river?
a. 29 s
b. 23 s
c. 25 s
d. 27 s
e. 17 s
d
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_____ is a constant in Einstein's equations of space and time that represents a force of repulsion
A) Planck's constant B) Cosmological constant C) Archimedes' constant D) Hubble's constant
Fluid Flow: Water is flowing in a drainage channel of rectangular cross-section. The width of the channel is 15 m, the depth of water is 8.0 m, and the speed of the flow is 2.5 m/s. What is the mass flow rate of the water? The density of water is 1000 kg/m3.
A. 2.0 × 105 kg/s B. 2.0 × 103 kg/s C. 3.0 × 105 kg/s D. 3.0 × 103 kg/s E. 3.0 × 102 kg/s
When did scientists first detect gravitational waves from mergers of compact objects (pairs of neutron stars or black holes)?
A) 2015 B) 1543 C) 1990 D) Gravitational waves have not yet been detected, though scientists hope to detect them soon.
A Styrofoam cooler has a surface area of 2,700 cm2 and a wall thickness of 3.0 cm. Styrofoam has a coefficient of thermal conductivity of 0.01 W/m C. A 2.0 kg block of ice is placed inside the cooler that has a temperature inside of 2.0
If the heat of fusion for ice is 333.7 kJ/kg and the temperature outside is 35.0
then how long will the ice last?
A. 74 hours B. 62 hours C. 55 hours D. 42 hours E. 24 hours