Question

An explosion blows a rock into three parts. Two parts go off at right angles to each other . These two are `1 kg` first part moving with a velocity of `12 ms^(-1) and 2 kg` second part moving with a velocity of `8 ms^(-1)`. If the third part flies off with a velocity of `4 ms^(-1)`. Its mass would be
A. `5 kg`
B. `7 kg`
C. `17 kg`
D. `3kg`

Answer 1

Apply law of conservation of linear momentum
Momentum of first part `= 1 xx 12 = 12 kg ms^(-1)`
Momentum of second part `= 2 xx 8 xx 16 kg ms^(-1)`
`:.` Resultant momentum
`= sqrt((12)^(2) + (16)^(2)) = 20 kg ms^(-1)`
The third part should also have same momentum
Let the mass of the third part be `M`, then
`4 xx M = 20`
`M = 5 kg`