Question

Express the kinetic energy in KJ when a bike of 80 kg moving with a velocity of 72km h-1

Answer 1

Kinetic Energy K=1/2 * m * v²

m=80 kg
v= 72 km/h= 20 m/s

K=1/2 * m * v²
∴K=1/2 * 80* 20²
      = 40*400
      = 16000 J

1 KJ= 1000 J
So 16000 J= 16 KJ

Answer 2

⇒ m = 80 kg

⇒ v = 72 × 5/18 = 20 m/s

⇒ Ek = 1/2 mv²

⇒ Ek = 1/2 × 80 × 20 × 20

⇒ Ek = 32000/2 = 16000J

⇒ Ek = 16kJ