Question

any one can solve it plss..An object A of mass 1kg is projected vertically upward with a speed of 20m/s. At the same moment another object B of mass 3kg, which is initially above the object A, is dropped from a height h=20m. The two point like objects collide and stick to each other. Find K.E of combined mass just after the collision???

Answer 1

Answer:50 J

Explanation:

mass of A =1 kg

mass of B=3 kg

they both collide at $t=\frac{20}{0+20}=1 s$ (using relative motion)

distance traveled by B in 1 s

$x=20\times 1-\frac{10\times 1^2}{2}=15 m$

velocity of B at x= 15 m  from floor

$v_b=10 m/s$

Velocity of A at $t=1 s$

$v_a=g\times 1$

$v_a=10 m/s$

by conserving momentum

$1\times 10-3\times 10=(1+3)v$

$v=\frac{-20}{4}=-5 m/s$

Kinetic energy of combined mass

$K.E.=\frac{4\times 5^2}{2}=50 J$