What is the kinetic Energy and the potential energy of an object with a mass 300g falling from a height of 200 cm? What is the final velocity just before it hits the ground if the object started from rest?

1 Answer
MattyMatty
Feb 17, 2018

#"Final velocity is "6.26" m/s"#
#E_p" and "E_k", see explanation"#

Explanation:

#"First we must put the measurements in SI units :"#
#m = 0.3 kg#
#h = 2 m#
#v = sqrt(2*g*h) = sqrt(2*9.8*2) = 6.26 m/s " (Torricelli)"#
#E_p "(at 2 m height) "= m*g*h = 0.3*9.8*2 = 5.88 J#
#E_k " (on the ground) "= m*v^2/2 = 0.3*6.26^2/2 = 5.88 J#
#"Note that we must specify where we take the "E_p" and "E_k"."#
#"At ground level "E_p = 0"."#
#"At 2 m height "E_k = 0"."#
#"In general at height h above the ground we have"#
#E_k = 0.3*9.8*(2-h)#
#E_p = 0.3*9.8*h#
#"So "E_p+E_k" is always equal to 5.88 J"#

#m = " mass in kg"#
#h = " height in m"#
#v = " velocity at ground level (final velocity)"#
#g = " gravity constant = 9.8 m/s²"#
#E_p = " potential energy"#
#E_k = " kinetic energy"#

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