# An object falls from rest possess 400J of kinetic energy at the end of 2sec. calculate the mass of the object

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Kinetic energy = 400 J

Time=2 s

Initial velocity, u=0

v = u + gt

v = 0 + 10 x 2 = 20 m/s

K = mv² = 400

× m × 20² = 400

m = 2 kg

The mass of the object is 2 kg.

{assuming g=10m/s}

Using the 1st eqn ,

V=u+gt

⇒v=0+10(2)

⇒v=20m/s.

KE=0.5mv²

⇒400=0.5m(400)

⇒m=2kg

Using the 1st eqn ,

V=u+gt

⇒v=0+10(2)

⇒v=20m/s.

KE=0.5mv²

⇒400=0.5m(400)

⇒m=2kg