Because radio waves can travel in space but sound waves cannot.
Answer:
Option D
The frequency
Explanation:
The speed of wave is depedant only on the wavelength and frequency of waves since it is given by s=fw where s is the speed, f is frequency and w is the wavelength. Since the options given has only one factor, that is frequency, hence option D is correct. In case we had wavelength could be among the options, both would be correct.
Answer:
b) 68,9 km/h a) picture
Explanation:
In this problem, since velocity is expressed in km/h and time in minutes, we have to convert either time to hours or velocity to km/min. It is easier to use hours.
Using this formula we pass time to hours:

Now we can plot speed vs time (image 1). The problem says that the driver uses constant speed, so all lines have to be horizontal.
Using the values of the speed we calculate the distance in each interval

Using these values and the fact that she was having lunch in the third one (therefore stayed in the same position), we plot position vs time, using initial position zero (image 2, distance is in km, not meters).
Finally, we compute the average speed with the distance over time:

Answer:
1) ironing a shirt 2) writing on surfaces 3) working of an eraser