Answer :
The height is 0.70 meters
The formula for gravitational potential energy is
= mgh
m= mass, g= acceleration due to gravity, h= height
54.9= 8 × 9.8 × h
54.9= 78.4h
h= 54.9/78.4
= 0.70 meters
Hence the height at which the bacpack was lifted is 0.70 meters
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