After burning through the thread, the first trolley weighing 600 g began to move at a speed of 0.4 m / s.

After burning through the thread, the first trolley weighing 600 g began to move at a speed of 0.4 m / s. Determine the mass of the second cart if it starts to move at a speed of 0.8 m / s.

Here is given in the SI system:
m1 = 600 g = 0.6 kg.
How many times the speed of the first body is greater than the speed of the second body, how many times the mass of the body is less than the mass of the second.
Let’s write this in the form of a formula:
v1 / v2 = m2 / m1
Let us define m2 from this expression:
m2 = v1 * m1 / v2
Let’s substitute the numerical values:
m2 = v1 * m1 / v2 = 0.4 * 0.6 / 0.8 = 0.3 kg
Answer: the mass of the second cart is 0.3 kg, or 300 g.