7. A freight train rolls along a track with a momentum p. Another freight train rolls with the same velocity, but has twice the mass of the first train How does the momentum of the second train compare to that of the first train? (Neglect friction] It is four times as much. It is twice as much. It is zero It is unchanged.

## Step 1: Understand momentum### Momentum is defined as , where is mass and is velocity.## Step 2: Compare masses### The first train has mass and the second train has mass .## Step 3: Compare velocities### Both trains move with the same velocity .## Step 4: Calculate the momentum for each train### Momentum of the first train .### Momentum of the second train .