before colliding, the momentum of block a is + 15.0 kg (m/s) and block b - 35.0kg (m/s). after block a has a momentum of - 12.0kg (m/s). what is the momentum of block b afterwards?

-8 Kgm/s

Explanation:

From the law of conservation of moentum, the sum of momentum before collision equals the sum of momentum after collision. Therefore

Before collision

Momentum = + 15 kgm/s+-35 kgm/s=-20 kgm/s

After collision

Momentum=-12 kgm/s + x kgm/s

x-12 kgm/s=-20 kgm/s

x=-20+12=-8 Kgm/s