First speed = 20km/h
Time = 3 hours
Distance = 3×20
<h3> = <u>60 km</u></h3>
Second speed = 30km/h
Time = 4 hours
Distance = 4×30
<h3> = <u>120 km</u></h3>
Total distance = 60+120 = <u>180km</u>
Total time = 3+4 =<u> 7 hours</u>
Average speed = 180/7
<h3> = <u>25.71</u><u> </u><u>km</u><u>/</u><u>h</u></h3>
Hope this will help...
The change in pitch of a train's horn as it passes while you are
standing still can be described by the Doppler effect, but that
doesn't explain it.
Answer:
The energy in its ground state is 10 meV.
Explanation:
It is given that,
The energy of the electron in its first excited state is 40 meV.
Energy of the electron in any state is given by :

For ground state, n = 1
.............(1)
For first excited state, n = 2
.............(2)
Dividing equation (1) and (2), we get :


So, the energy in its ground state is 10 meV. Hence, this is the required solution.
Answer: Blake may have a decreased chance of disease.
Explanation:
Research has shown that on average, a person who engages in more physical activity will live longer than a person who does not with one reason for this being that engaging in physical activity helps reduce the risk of diseases such as; heart disease, diabetes, and many forms of cancer.
Obesity (risk factor) and high blood pressure are also reduced by engaging in physical activity.
Density of a material depends upon it's mass & volume.
You can calculate it by: Density = Mass / Volume
Hope this helps!