Answer: 85.4 km/h
Step-by-step explanation:
We would apply the law of conservation of kinetic energy. The formula is expressed as
KE1 + PE1 = KE2 + PE2
where
KE1 and KE2 are the initial and final kinetic energies
PE1 and PE2 are the initial and final potential energies
The formula for calculating kinetic energy is
KE = 1/2mv^2
where
m is the mass of the object
v is the velocity
The formula for calculating potential energy is
PE = mgh
where
g is the acceleration due to gravity = 9.8m/s^2
h is the height of the object
From the information given,
m = 55
h = 8.3
Potential energy at the top = 55 x 9.8 x 8.3 = 4473.7
At the top, v = 72km/h
Recall, 1 km = 1000m
1 hour = 3600s
72km/h = 72 x 1000/3600 = 20m/s
kinetic energy at the top = 1/2 x 55 x 20^2 = 11000
KE1 + PE1 = 4473.7 + 11000 = 15473.7
At the point of landing,
PE2 =0
KE = 1/2 x 55 x v^2 = 27.5v^2
Thus,
27.5v^2 = 15473.7
v^2 = 15473.7/27.5
v = √(15473.7/27.5)
v = 23.72 m/s
his landing speed is 23.72 m/s
Converting to km/h, we would multiply 23.72 by 18/5
Landing speed = 85.4 km/h