Question

A mass of 1 kg is thrown up with velocity of 100 m/s. After 5 second it explodes into 2 parts. One part of mass 400 g move down with a velocity 25 m/s. Calculate the velocity of other part just after explosion?? (g=10 m/s²)

Answer 1

After `5s` of throwing the whole mass will have a velocity of `v=100-(10×5)=50 ms^-1` (using ,`v=u-g t`)

Now,let the other mass will move with velocity `v`

So,considering upward velocity to be positive,we can say momentum after the explosion will be,

`(400/1000 ×(-25) + 600/1000 ×v) Kg ms^-1`

And,momentum before the collision was `1×50 Kg ms^-1`

Now,applying law of conservation of momentum we get,

`1×50=-0.4×25 +0.6×v`

Or, `v=100 ms^-1`

So,the other mass will go upwards with a velocity of `100 ms^-1`

Note here we considered that for a time being external force gravity had no effect on the motion of the two objects,so we did apply the law of conservation of momentum.