Two balls are thrown simultaneously,A vertically upwards with a speed of 20m/s from the ground and B vertically downwards from a height of 40m with the same speed and along the same line of motion at what paints do the two balls collide?
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Answer:
l would recommend you study reference frames before attempting such questions, it shall make these exponentially easier. however, if you're already studying them, and were stuck on this question, here's the solution, which should also help resolve some common misconceptions i've seen students alike have.
let's assume the reference frame of any ball, say.. Ball A. from this RF, since Ball B and Ball A have the same acceleration 'g,' we need not account for the acceleration, in solving time period. for the balls to meet, the two must've covered a combined total of 40 metres, but from our RF, ball 'B' must've covered these 40 metres with a speed (20 + 20)m/s, or.. in 40/40, or 1 second.
now that we know the value of the time in which the two balls meet, we can calculate the distance at which they meet. from the top, this distance will be equal to the distance travelled by the ball thrown at 20m/s in 1 second, or, it will be equal to (20)(1) + (1/2)(g)(1^2) = 20 + 4.9 = 24.9 metres. or, from the bottom, (40 - 24.9) metres, which is equal to 15.1 metres.