A21.0 kg shopping cart is moving with a velocity of 4.0 m/s. it strikes a 9.0 kg box that is initially at rest. they stick together and continue moving at a new velocity. assume that friction is negligible. what was the momentum of the shopping cart before the collision? 0 kg⋅m/s 36 kg⋅m/s 168 kg⋅m/s 84.0 kg⋅m/s what was the momentum of the box before the collision? 168 kg⋅m/s 84.0 kg⋅m/s 0 kg⋅m/s 36 kg⋅m/s what is the velocity of the combined shopping cart–box wreckage after the collision? 9.3 m/s 4.0 m/s 2.8 m/s 0 m/s