Question

A stone thrown downward with a speed of 15.7 m/s from a height of 12.7 m above the ground has a kinetic energy of 293 Joules when it is 1.29 m above the ground. What is the mass of the stone?

Answer 1

Explanation:

• Mechanical Energy = Constant

Assuming P.E. at 1.29m to be zero. :

=> K.E.( at 12.7m ) + P.E.( at 12.7m ) = K.E.( at 1.29m )

=> 0.5m( 15.7 )^2 + m( 9.8 )( 12.7 - 1.29 ) = 293

=> 235.063m = 293

=> m = 293 / 235.063 = 1.24kg ( approx. )