Q: Why are distances in space often measured in light years?
2 answers:
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Answer:
(a) 89 m/s
(b) 11000 N
Explanation:
Note that answers are given to 2 significant figures which is what we have in the values in the question.
(a) Speed is given by the ratio of distance to time. In the question, the time given was the time it took the pulse to travel the length of the cable twice. Thus, the distance travelled is twice the length of the cable.
(b) The tension, , is given by
where is the speed,
is the tension and
is the mass per unit length.
Hence,
To determine , we need to know the mass of the cable. We use the density formula:
where is the mass and
is the volume.
If the length is denoted by , then
The density of steel = 8050 kg/m3
The cable is approximately a cylinder with diameter 1.5 cm and length or height of 620 m. Its volume is
The wind tunnel speed that must be used to test the car 1 / 5 model of a car that normally runs at 30 mph is 150 mph
Re = u L / ν
Re = Reynold's number
u = Flow speed
L = Characteristic linear dimension
ν = Kinematic viscosity
ν = 1.516 *
m² / s
ν = ν
= 1.516 *
m² / s
L = L
/ 5
u = 30 mph
Re = u
L
/ 5 * 1.516 *
Re = 30 L
/ 1.516 *
In tunnel,
Re = Re
u L
/ 5 * 1.516 *
= 30 L
/ 5 * 1.516 *
u = 30 * 5
u = 150 mph
Therefore, the wind tunnel speed that must be used to test the car is 150 mph
To know more about Reynold's number
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