The pilot of an aircraft flies due north relative to the ground in a wind blowing 40 km/h toward the east. If his speed relative to the ground is 80 km/h, what is the speed of his airplane relative to the air?
a. 89 km/h
b. 85 km/h
c. 81 km/h
d. 76 km/h
e. 72 km/h
a
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Air at 20°C flows at 1 m/s between two parallel flat plates spaced 5 cm apart. Estimate the distance from the entrance to the point at which the hydrodynamic boundary layers meet.
GIVEN
Air flows between two parallel flat plates
Air speed (U?) = 1 m/s
Distance between the plates (D) = 5 cm = 0.05 m
Air temperature = 20°C
FIND
The distance from the entrance (X1) where the boundary layers meet
ASSUMPTIONS
Steady state
Laminar flow
SKETCH
A simple pendulum, 2.00 m in length, is released from rest when the support string is at an angle of 35.0° from the vertical. What is the speed of the suspended mass at the bottom of the swing? (g = 9.80 m/s2 and ignore air resistance)
a. 0.941 m/s c. 2.66 m/s b. 1.88 m/s d. 1.33 m/s
In what way do observations of binary star systems support the special theory of relativity?
A) Stars in binary systems often orbit at speeds close to the speed of light, allowing us to check whether time dilation really occurs. B) Stars in binary systems are moving, so we can compare their moving masses to their rest masses. C) The fact that the stars appear distinct supports the idea that the speed of light is unaffected by the motion of the stars. D) Binary systems have two stars, and therefore give us twice the opportunity to test the theory than single star systems.
A mass is bouncing on the end of a spring with a period T when measured by a ground observer. What would the period of oscillation be (as measured by the same observer) if the mass and spring were moving past the ground observer at a speed of 0.600c?
a. 0.440 T b. 1.25 T c. 0.600 T d. 1.67 T