8. a train rolls at a constant speed of 10 m/s across a horizontal track. a child standing on the flatbed of the
train throws a ball so that it appears to move straight up to an observer standing next to the track.
a. what is the horizontal speed of the ball relative to the observer?
b. what is the horizontal speed of the ball relative to the train?
c. if the ball is also thrown upward with a speed of 20 m/s, what is the overall initial speed of the ball
relative to the train?

This is important 1. what happens to the speed of molecules in water vapor when it condenses to form a liquid? (2 points) the molecules slow down. the molecules speed up. the molecules slow down and then speed up. the molecules speed up and then slow down. 2. how might human activities change to compensate for a decrease in water supplies? (2 points) humans might build a factory. humans might build drainage systems. humans might extract more water from the ground. human behavior does not change because of the water cycle. i'll be grateful if anyone can answer these 2 questions !

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.

Cyclotrons are widely used in nuclear medicine for producing short-lived radioactive isotopes. these cyclotrons typically accelerate h- (the hydride ion, which has one proton and two electrons) to an energy of 5 mev to 20 mev. this ion has a mass very close to that of a proton because the electron mass is negligible—about 1 2000 of the proton’s mass. a typical magnetic field in such cyclotrons is 1.9 t. (a) what is the speed of a 5.0-mev h-? (b) if the h- has energy 5.0 mev and b = 1.9 t, what is the radius of this ion’s circular orbit?