Answered By Merna A

Hi,

These are the equations requied to answer this question:

1. PE ( potenial energy ) = m ( mass )* g(gravity) * h ( height).

2. KE ( kinetic energy) = 0.5 * m ( mass) * v^2( velocity squared).

3. Initial PE + Initial KE= Final PE + Final KE

Initially, before the object starts falling.

m= 10 kg ; h =20 m; v=0 m/s; g=9.81 m/s2

The initial PE= (10 kg) * 9.81m/s2 * 20 m = 1962 J

The inital KE = 0.5 * 10* (0m/s )^2= 0 J

Finally, in the middle of the flight

m= 10 kg, h =10 m, v= ?, g=9.81 m/s2

Final PE= ( 10 kg) ( 9.81 m/s2) ( 10)= 981 J

Final KE = ?  ( we can find it using the third equation in the above mentioned list: Initial PE + Initial KE= Final PE + Final KE).

Inital PE= 1962 J

Initial KE= 0 J

Final PE= 981 J

Final KE= Initial PE +Initial KE- Fianl PE = 1962 J + 0J - 981 J= 981 J

To find v ( speed) you will have to isolate v from the KE equation 

v= sqrt ( 2KE/ m)= 14 m/s

 

I hope this answer is helpful!!

Best of luck