Question

A 2kg mass is moving on a frictionless airtrack. It collides into a motionless 1.5 kg mass.
What is the combined speed of the two masses if they stick together on impact

Answer 1

Answer:

$0.57v_1$

Explanation:

From the law of conservation of momentum, the sum of initial momentum equals the sum of final momentum

Momentum, p=mv where m is the mass and v is the velocity

$m_1v_1+m_2v_2=(m_1+m_2)v_c$ where $v_c$ is the common velocity, $v_1$ and $v_2$ are velocities of 2 Kg moving mass and motionless 1.5 kg mass respectively, $m_1$ and $m_2$ are masses of 2 Kg moving mass and motionless 1.5 kg mass .

Since the 1.5 Kg mass is motionless, it's velocity is zero hence

$m_1v_1=(m_1+m_2)v_c$

By substitution

$2v_1=(2+1.5)v_c$

$2v_1=3.5v_c$

$v_c=\frac {2v_1}{3.5}=0.571428571v_1\approx 0.57v_1$