Answer:
Gravitational potential energy = (mass) x (gravity) x (height)
Kinetic energy (of a moving object) = (1/2) (mass) x (speed)²
When the pendulum is at the top of its swing, its potential energy is
(mass) x (gravity) x (height)
= (5 kg) x (9.8 m/s²) x (0.36 m)
= (5 x 9.8 x 0.36) joules
17.64 joules .
Energy is conserved ... it doesn't appear or disappear ... so that number is exactly the kinetic energy the pendulum has at the bottom of the swing, only now, it's kinetic energy:
17.64 joules = (1/2) x (mass) x (speed)²
17.64 joules = (1/2) x (5 kg) x (speed)²
Divide each side by 2.5 kg:
17.64 joules / 2.5 kg = speed²
Write out the units of joules:
17.64 kg-m²/s² / 2.5 kg = speed²
(17.64 / 2.5) (m²/s²) = speed²
7.056 m²/s² = speed²
Take the square root of each side: Speed = √(7.056 m²/s²) = 2.656 m/s.
Looking through the choices, we're overjoyed to see that one if them is ' 2.7 m/s '. Surely that's IT !
Hope this will help you ...