Solve the following sql problem:
How many cars are there on train no.1?

Schema:
SCHEMA:
- Table: cars
  - Column: id
    - Samples: [1, 2, 3, 4, 5]
  - Column: train_id
    - Samples: [1, 1, 1, 1, 2]
  - Column: position
    - Samples: [1, 2, 3, 4, 1]
  - Column: shape
    - Samples: [rectangle, rectangle, rectangle, rectangle, rectangle]
  - Column: len
    - Samples: [short, long, short, long, short]
  - Column: sides
    - Samples: [not_double, not_double, not_double, not_double, not_double]
  - Column: roof
    - Samples: [none, none, peaked, none, flat]
  - Column: wheels
    - Samples: [2, 3, 2, 2, 2]
  - Column: load_shape
    - Samples: [circle, hexagon, triangle, rectangle, circle]
  - Column: load_num
    - Samples: [1, 1, 1, 3, 2]
- Table: trains
  - Column: id
    - Samples: [1, 2, 3, 4, 5]
  - Column: direction
    - Samples: [east, east, east, east, east]

SELECT COUNT(id) FROM cars WHERE train_id = 1