In answer to your question, it first depends on the condition of the coin. In evaluating your coin, the following degrees will be used to measure it's worth.
- Fine (F): This is generally quite worn out, but the coin itself is intelligible. This would receive the lowest possible value.
- Very Fine (VF): The detail is still clear here, but there is a lot of obvious wear. High spots are still visible, but condition is not excellent.
- Extremely Fine (EF): This can appear uncirculated by an untrained professional. Generally excellent condition, until inspected very closely.
- Uncirculated (Unc): Absolutely no wear at all, in mint condition.
So depending on the condition of your coin, you will receive different values. With that being said, the 1940's 50 US cents would have been the Walking Liberty Half Dollar. Estimations of the value of this coin range from roughly $8 - $9 in Fair condition, to around $40 for uncirculated condition. I hope this answers your question.