Two students want to investigate the conservation of linear momentum during an "explosion" event on a horizontal low-friction track.
They place two carts, P P\,P and QQQ, in contact and at rest. Cart P P\,P has a spring-loaded plunger which, when released, pushes the carts apart in opposite directions.
Each cart is fitted with an interrupting card of length LLL.
Two light gates are positioned on either side of the starting position: Light Gate 1 to detect the passage of Cart P P\,P as it moves to the left, and Light Gate 2 to detect the passage of Cart Q Q\,Q as it moves to the right.
Describe an investigation the students could carry out to show that momentum is conserved during this interaction.