Barron's 2nd Edition PT1 Q41

Barron's Book

41) For this question, we want to find the speed of the block of mass m. If we use the conservation of momentum, this problem becomes fairly simple. We can start by looking at the momentum before the carts are released.

Where p is momentum, v is velocity, and m is mass

Next, we’ll look at the momentum after the carts are released.

Where p is momentum, m is mass, and v is velocity

We still don’t know the speed on the cart with mass m. Since momentum is conserved, we can equate the system’s momentum at both points of its motion.

Where p is momentum, m is mass, and v is velocity

Answer: E