# An autographed baseball rolls off of a 1.4 m high desk & strikes the floor .53 m away from the desk. How fast was it. . .rolling on the desk before it fell off? The accel. of gravity is 9.81...

An autographed baseball rolls off of a 1.4 m high desk & strikes the floor .53 m away from the desk. How fast was it. . .

rolling on the desk before it fell off? The accel. of gravity is 9.81 m/s^2.

My original answer was 3.2 but was told that was wrong. What did I do wrong?

ndnordic | High School Teacher | (Level 2) Associate Educator

Posted on

The key is to determine how long  it took the ball to fall from the desk to the floor.

The relationship is:

delta y = Viy + 1/2 gt^2

When the ball rolls off the edge of the table, the initial velocity in the y-direction (Viy) is assumed to be zero.

So, it simplifies to:  delta y = 1.2 gt^2

delta y = 1.4 m, g = 9.81 m/s/s and solve for t.

t = 0.53 s.

In 0.53 s, the ball went forward 0.53 m.

velocity = d/t = 0.53 m/0.53s = 1.0 m/s ball speed in the x-direction when it rolled off the table.