JEE MAIN - Physics (2002 - No. 55)
From a building two balls A and B are thrown such that A is thrown upwards and B downwards ( both vertically with the same speed ). If vA and vB are their respective velocities on reaching the ground, then
$${v_B} > {v_A}$$
$${v_A} = {v_B}$$
$${v_A} > {v_B}$$
their velocities depend on their masses.
Explanation
Assume the initial velocity of each particle is = u
And height of building = h
If final velocity of A is vA then vA2 = u2 + 2(-g)(-h) = u2 + 2gh
If final velocity of B is vB then vB2 = u2 + 2gh
$$\therefore$$ vA = vB
Sign Rule : Take the direction of initial velocity positive opposite direction as negative.
Here for ball A initial velocity u is upward so upward is positive and downward is negative. That is why gravity is = - g and height = - h
And for ball B initial velocity u is downward so downward is positive and upward is negative. That is why gravity is = + g and height = + h
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