Question

Which falling object has the least kinetic energy when it collides on the ground?

(3 points)
Responses

120 kg of sand falling 12 m/s
120 kg of sand falling 12 m/s

12 kg of sand falling at 8 m/s
12 kg of sand falling at 8 m/s

12 kg of water falling at 10 m/s
12 kg of water falling at 10 m/s

120 kg of water falling at 12 m/s
120 kg of water falling at 12 m/s

Answer 1

Kinetic energy KE = 1/2 mv^2. Compute each:

- 120 kg at 12 m/s: KE = 0.5·120·12^2 = 8640 J
- 12 kg at 8 m/s: KE = 0.5·12·8^2 = 384 J
- 12 kg at 10 m/s: KE = 0.5·12·10^2 = 600 J
- (120 kg at 12 m/s) = 8640 J

Least KE = 384 J, so the 12 kg of sand falling at 8 m/s.