The lifetime of a ?+ meson normally is 18 nanoseconds. In a large particle accelerator, scientists can create ?+ mesons moving at speeds close to the speed of light. What do the scientists observe when they measure the lifetime of a ?+ meson that is created at high speed?
A) The ?+ meson lasts much more than 18 nanoseconds.
B) The ?+ meson lasts 18 nanoseconds.
C) The ?+ meson lasts much less than 18 nanoseconds.
D) The ?+ meson no longer decays and remains as a stable particle.
A) The ?+ meson lasts much more than 18 nanoseconds.
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A hot-wire anemometer is used to determine the boundary layer velocity profile in the air flow over a scale model of an automobile. The hot-wire is held in a traversing mechanism that moves the wire in a direction normal to the surface of the model. The hot-wire is operated at constant temperature. The boundary layer thickness is to be defined as the distance from the model surface at which the velocity is 90% of the free stream velocity. If the probe current is I0, when the hot-wire is held in the free stream velocity, U?, what current indicates the edge of the boundary layer? Neglect radiation heat transfer from the hot-wire and conduction from the ends of the wire.
GIVEN • Thin, electrically-heated constant-temperature wire in air flow near an automobile model • Boundary layer thickness ° point when velocity (Uy) = 90% free stream velocity Vo • Probe current at U? = Io FIND • Probe current at edge of the boundary layer (Ib) ASSUMPTIONS • Radiation is negligible • Conduction from the ends of the hot-wire is negligible • Reynolds number is small
Suppose that we place an aluminum cylinder, a wooden block, and a Styrofoam cup on a table and leave them there for several hours. We then come back into the room and feel each object. (a) Which (if any) feels coolest?
A. The aluminum cylinder B. The wooden block C. The Styrofoam cup D. All are the same.
When you are standing by an air conditioning vent in an indoor swimming pool area, you feel a lot cooler if you are wet than if you are dry. Why?
What will be an ideal response?
According to our theory of solar system formation, which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size?
A) Newton's third law B) the law of conservation of angular momentum C) the law of conservation of energy D) the two laws of thermal radiation