Question

A solid cast-iron sphere (? = 0.256 lbm/in³ (7090 kg/m³)) of 10 in. (25 cm) diameteter travels without friction at 30 ft/s (9 m/s) horizontally. What is its kinetic energy?

1900 ft-lbf (2.4 kJ)                                 c. 1200 ft-lbf (1.6 kJ)

1600 ft-lbf (2.0 kJ)                                 d. 900 ft-lbf (12 kJ)

Answer 1

Diameter of sphare d = 25 cm = 0.25 m ( 1 m=100 cm)

volume of the sphare =   Volume = *0.25³/6 = 0.008 m³, density of sphare = 7090 Kg/m³

Mass of sphare = volume * density = 0.008 m³ *7090 Kg/m³ = 58 Kg

V = velocity = 9 m/s

Kinetic Energy = 1/2 * 58 Kg*9² m/s = 2349 Jule = 2.349 KJ = 2.4 Kj ( round figure)

Option (a) is correct