no, it not useless. we still learn Bohr's model in HS n dats almost 200 yr old! while there may be new models, previous one is good for explaining the basics. it is also useful to learn previous model n see how our understanding improves over time.
Force equals mass*distance
F = ma
Given m = 10 kg, F = 30 N
30 = 10a
30/10 = a
3 = a
The wagon's acceleration is 3 m/s^2
You should put when you will leave, where you will be, and what time you will get back.
De broglie wavelength, 
, where h is the Planck's constant, m is the mass and v is the velocity.
Mass of hydrogen atom, 
v = 440 m/s
Substituting
Wavelength 
So the de broglie wavelength (in picometers) of a hydrogen atom traveling at 440 m/s is 902 pm
The electromagnetic spectrum includes a continuous spectrum of wavelengths that include:
Radio waves, microwaves, infrared light, visible, ultraviolet, X-rays, gamma rays
The wavelength decreases from radio waves to gamma rays, whereas the energy increases along the same direction.
In the given example, radio waves have a lower energy and higher wavelength than visible light. The latter can be perceived by the human eye, whereas radio waves are not visible to the human eye.
1) They have colors = visible light
2) They can travel in a vacuum = both
3) They have energy = both
4) They’re used to learn about dust and gas clouds = radio waves
5) They’re used to find the temperature of stars = visible light
6)They’re invisible = radio waves
