Question

Lars is standing near the edge of a 90-meter cliff. He throws a ball upward, but does not catch it, and it falls to the bottom of the cliff face. From when he threw the ball upward to when it hit the ground below, 5.55 seconds passed. What was the initial vertical velocity of Lars' throw?
a. -43 m/s
b. -11 m/s
c. 43 m/s
d. 11 m/s

Answer 1

Answer:

c. 43 m/s

Explanation:

Given the following data;

Displacement, S = 90 meters

Time, t = 5.55 seconds

To find the initial velocity;

We would use the second equation of motion given by the formula;

$S = ut + \frac {1}{2}at^{2}$

Where;

• S represents the displacement or height measured in meters.

• u represents the initial velocity measured in meters per seconds.

• t represents the time measured in seconds.

• a represents acceleration measured in meters per seconds square.

We know that acceleration due to gravity is -9.8m/s² because the direction is downward.

Substituting into the equation, we have;

$90 = u*5.55 + \frac {1}{2}*(-9.8)*5.55^{2}$

$90 = u5.55 - 4.9*30.8025$

$90 = u5.55 - 150.93225$

Rearranging the equation, we have;

$u5.55 = 90 + 150.93225$

$u5.55 = 240.93225$

$u = \frac {240.93225}{5.55}$

Initial velocity, u = 43.41 ≈ 41 m/s