Dynamics Cart (Pair) SE. 

Because these large, high impact resistant carts have accurately aligned axles, they yield superior data for all quantitative kinematics experiments. 
With a low profile and three widely spaced wheels for stability, each features a Velcro attachment for studying inelastic collisions and an easily set firing mechanism with two firing positions.
The carts can be towed with rubber bands to simulate the application of constant forces. Also features a non-slip vinyl surface for holding additional weight and a safety catch to lock during storage. 
Stackable, each cart can support over 132 lb. Includes instructions with theory.
Length 300xwidth 120x100mm
Weight 600gms each