物理加英文问题：Two rocks are tied together with a string of negligi

物理加英文问题：Two rocks are tied together with a string of negligible mass,
and thrown into the air. At a
particular instant, rock 1, which has a mass of
0.1 kg, is moving with velocity v1 = （6, −5, 4）
m/s, and rock 2, which has a mass of 0.35 kg,
is moving with velocity v2 = （−7, 3, 2） m/s.
What is the magnitude of the momentum
of the system of the two rocks?
Answer in units of kg · m/s