Question

A toy aeroplane of mass $m_a=3\text{kg}$ is moving with a velocity of $10\text{m/s}$ in a horizontal direction. If a bird of mass $m_b=2\text{kg}$ sits on the toy aeroplane, find the final velocity of (toy+bird) system.(Initial velocity of the bird is zero.)

• A. $6\text{m/s}$
• B. $4\text{m/s}$
• C. $3\text{m/s}$
• D. $2\text{m/s}$

Answer 1

The correct option is A $6\text{m/s}$

Given:
Mass of toy aeroplane; $m_a=3\text{kg}$
Mass of bird; $m_b=2\text{kg}$
Initial velocity of toy aeroplane; $v_a=10\text{m/s}$
Initial velocity of bird; $v_b=0\text{m/s}$
Let final velocity of (toy+bird) system is $v_f$
As there is no net external force in horizontal direction.
$\therefore p_i=p_f$
$\Rightarrow m_a{v}_a=(m_a+m_b)v_f$
$\Rightarrow v_f=\frac{m_a{v}_a}{m_a+m_b}=\frac{(3\times 10)}{2+3}\text{m/s}=6\text{m/s}$