A few days ago
Anonymous

physics home work please help?

A ball is thrown upward from the ground with an initial speed of 31 m/s. At the same instant, a ball is dropped from rest from a building 15 m high. After how long will the balls be at the same height?

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I graphed the movement of the two objects and put the point of intersection as the answer, but the webassign.net program said it was wrong. What do I have to do to solve this

Top 1 Answers
A few days ago
Dominic D

Favorite Answer

what answer DID you get? (that would help with answering your Q).

did you use the following equation for height vs. time?

y = yo + vo*t – (1/2)g*t^2

where g = 9.81 m/s

1st ball:

yo = 0 m

vo = +31 m/s

2nd ball

yo = 15 m

vo = 0 (from rest)

so: y1 = 31t – (1/2)gt^2

y2 = 15 – (1/2)gt^2

set them equal to each other .. that’s when they are at the same height.

….and solve for t.

g.l.

d

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