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Solving freefall problems using kinematic formulas

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A squirrel drops an acorn onto the head of an unsuspecting dog. The acorn falls 4, point, 0, start text, m, end text before it lands on the dog. We can ignore air resistance.
How many seconds did the acorn fall?
Round the answer to two significant digits.
Answer using a coordinate system where upward is positive.
  • Your answer should be
  • an exact decimal, like 0, point, 75
start text, s, end text