motion ~ Help ~

用500n ge去力拉/推那個car:一次性用500N推一推那個car

如果題目話..A man act a force of 500N on a car with constant speed,
咁就係那個man是一直用500N的force去拉/推那個car

Under normal circumstances, your sentence would mean a force of 500 N is exerted on the car by the man CONTINUOUSLY (the wordings of your sentence is in fact a little bit odd, it should be written as: a man exerts a force of 500 N to push/pull a car, or a car is pulled/pushed by a man with a force of 500N).
In the case that the force is exerted only on short duration, normally the [duration] at which the force acted would be stated.