Business Green: US electric car firm Tesla Motors has taken another major step towards the mainstream, announcing plans for an $100m IPO which would make it the first US car firm to go public since Ford in 1956. As widely anticipated the California-based company filed documents with the US Securities and Exchange Commission (SEC) late on Friday, which confirmed it was looking to raise $100m at an IPO but failed to provide details on the proposed timing and pricing of the floatation. The …