Now, it will be clear from the following animation that when the 30kg mass goes up by a distance of x , the 20 kg mass will move down by a distance of 2x. Hence, if the acceleration of 30kg mass is a (upward), the acceleration of 20kg mass will be 2a (downward).

Applying Newton's law to mass of 20 kg,

-T + 20 × 9.81 =20 × 2a ..........................(i)

Kinetics of a Particle
		Let us solve this problem. Making the free body diagram of 20 kg mass.


Now, it will be clear from the following animation that when the 30kg mass goes up by a distance of x , the 20 kg mass will move down by a distance of 2x. Hence, if the acceleration of 30kg mass is a (upward), the acceleration of 20kg mass will be 2a (downward). Applying Newton's law to mass of 20 kg, -T + 20 × 9.81 =20 × 2a ..........................(i)