The frequency of a wave is the number of waves that passes through a point in a certain time. The less waves that pass in a period of time the lower the frequency of the wave. The more waves that pass in a period of time the higher the frequency of the wave. When measuring wave length the time period used is usually one second.
Answer:
A body travels 10 meters during the first 5 seconds of its travel,and a total of 30 meters over the first 10 seconds of its travel
20miles / 5sec = 4miles /sec would be the average speed for the last 20 m
Explanation:
The answer is 4 m/s.
In the first 5 seconds, a body travelled 10 meters. In the first 10 seconds of the travel, the body travelled a total of 30 meters, which means that in the last 5 seconds, it travelled 20 meters (30m + 10m).
The relation of speed (v), distance (d), and time (t) can be expressed as:
v = d/t
We need to calculate the speed of the second 5 seconds of the travel:
d = 20 m (total 30 meters - first 10 meters)
t = 5 s (time from t = 5 seconds to t = 10 seconds)
Thus:
v = 20m / 5s = 4 m/s
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Answer:
For areas marked X, Y, Z, X is attractive only, Y has a very small range, and Z is attractive and repulsive
Explanation:
Solution
Given that:
From the question stated, Anna drew a diagram to compare forces that are strong and weak.
Now,
We are to find which labels are grouped in areas marked as X, Y, Z respectively.
Thus,
For X, Y, Z it is marked as:
X: Always attractive or attractive only
Y: Very small range
Z: Repulsive and attractive
Answer:
- 3 cm
Explanation:
From the mirror formula;
1/f = 1/v + 1/u ; where f is the focal length, v is the image distance, and u is the object distance.
1/-4.5 = 1/9 + 1/v
1/v = -1/4.5 - 1/9
= -1/3
Therefore;
v = -3 cm
Hence;
Image distance is - 3cm
<h2>
Answer: 0.17</h2>
Explanation:
The Stefan-Boltzmann law establishes that a black body (an ideal body that absorbs or emits all the radiation that incides on it) "emits thermal radiation with a total hemispheric emissive power proportional to the fourth power of its temperature":
(1)
Where:
is the energy radiated by a blackbody radiator per second, per unit area (in Watts). Knowing 
is the Stefan-Boltzmann's constant.
is the Surface area of the body
is the effective temperature of the body (its surface absolute temperature) in Kelvin.
However, there is no ideal black body (ideal radiator) although the radiation of stars like our Sun is quite close. So, in the case of this body, we will use the Stefan-Boltzmann law for real radiator bodies:
(2)
Where 
is the body's emissivity
(the value we want to find)
Isolating from (2):
(3)
Solving:
(4)
Finally:
(5) This is the body's emissivity
