Two objects, one of mass 4 kg and the other of mass 20 kg, are dropped from the

Question

Two objects, one of mass 4 kg and the other of mass 20 kg, are dropped from the top of a building. When they hit the ground (neglecting air resistance), _____.

       both will have the same kinetic energy
       the heavier one will have one fifth the kinetic energy of the lighter one
       the heavier one will have half the kinetic energy of the lighter one
       the heavier one will have twice the kinetic energy of the lighter one
       the heavier one will have five times the kinetic energy of the lighter one

A 6 kg ball moving in the +x direction at 3 m/s collides head-on with a 3 kg ball initially at rest. The collision is inelastic. After the collision, the 3 kg ball is traveling at 2m/s in the +x direction. The velocity of the 6 kg ball after the collision is

       4 m/s    x with caret on top
       3 m/s    x with caret on top
       2 m/s    x with caret on top
       -3 m/s    x with caret on top
       None of the above

Neglecting air resistance, which is the approximate speed of an object that is dropped from rest, after it has fallen 7.2 m?

       11.9 m/s
       8.8 m/s
       7.3 m/s
       6.9 m/s
       None of the above

Two objects, one of mass 4 kg and the other of mass 20 kg, are dropped from the top of a building. When they hit the ground (neglecting air resistance), _____.

Explanation / Answer

1) The heavier one will have 5 times more kinetic energy than the lighter one. as they are dropped from the same height so the heavier one will have 5 time potential energy than the lighter one and ehile reaching the ground all the PE will be convetrted to KE resulting it to be 5 times higher than the lighter one.

2)given the collision is inelastic

and momentum will be conserved after the collision

=> 6*3 = 6*v + 3*2

=> v = 2 m/s so option 3 is correct.

3) Total energy will be conserved and as dropped from initial zero speed => 0 KE

let after falling 7.2 meter it has speed v

=> 0.5*m*v^2 = m*g*7.2

=> v = sqrt(g*7.2*2) = 11.9 m/s option 1 is correct

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