Question

A 1.25 lbs. measuring tape became dislodged from the belt of a worker on the 48^th floor of a building under construction and fell approximately 460 feet hitting another worker who was delivering materials to the project.  The worker who was struck and killed was not wearing a hard hat but had one available in his truck.  If we assume a deceleration distance of 4”, what was the force in pounds generated by the measuring tape at impact?  (3)  Bonus pt. for calculating the velocity of the tape at impact.  (1)

Answer 1

Answer,

The final velocity of the measuring tape is

Here, g is the acceleration ue to gravity, equal to 32.174 ft/s2

Putting these in our equation, we get

To find the force when it decelerates, we need to find the deceleration. We can find the deceleration using a similar formula to above.

Here, S is the distance over which it declerates, i.e 4in = 0.33ft

Putting these in our equation, we get

Since a pound-force is equal to the mass in pounds time the acceleration due to gravity, we'll express our acceleration in terms of gravity.

Therefore, the force exerted by the tape measure is