There is provided a cart for lifting and moving materials. The cart includes a lift mechanism for raising and lowering a support surface to lift the materials during transport. The cart also includes a motorized drive wheel assembly which provides a drive force in a forward or backward direction to assist the operator in moving the materials. The motorized drive wheel assembly has a variable vertical position relative to the cart wheels to enable the drive wheels to provide a drive force over contoured surfaces, such as near the base or top of a ramp. The motorized drive wheel assembly also includes a weight to maintain a minimum normal force for traction and includes a differential to allow the drive wheels to rotate at differing speeds to facilitate convenient steering of the cart. The cart is powered by one or more rechargeable batteries.