A pelican flying along a horizontal path drops a fish from a height of 4.6 m, the fish travels 6.8 m horizontally before it hits the water below. What was the pelican's speed?

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justaguide | College Teacher | (Level 2) Distinguished Educator

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To determine the pelican's initial speed we first need to determine the time that elapsed before the fish hit the water.

The fish was dropped from a height of 4.6 m and it only had a horizontal velocity initially. The acceleration due to gravity is 9.8 m/s^2. The relation between the initial velocity, acceleration, time and distance traveled for an object is s = u*t + (1/2)a*t^2

=> 4.6 = 0*t + (1/2)*9.8*t^2

=> t^2 = 4.6*2/9.8

=> 46/49

=> t = (sqrt 46)/7 s

The fish hit the water after (sqrt 46)/7 seconds. In this duration of time it traveled 6.8 m horizontally.

The horizontal speed of the fish was 6.8*7/sqrt 46 = 7.01 m/s.

As the fish had the same horizontal speed as the pelican that dropped it, the speed of the pelican was also 7.01 m/s