Go to the Uranus Zone and go to the UFO Crash Ride. Remove all the barriers around it and then go to the nearby rocket kiosk, Rockets Red, just past the clown car next to the swinging ship and get some firecrackers. Simply throw them around the UFO crash to attract the zombies. When you can see a horde around it look to the right of the ride to see some railing and a podium, this is where you launch the ride. Run to the podium and activate the ride and this should kill more than 10 zombies.