An electric car can go 150 km on a test track at a constant speed of 100 km/hr on one charge of its batteries. The test track is an oval with no stops or other cars. You can assume that air resistance is the only form of friction. How far can it go on the test track if it moves at a constant speed of 50 km/hr?

75km

Explanation:

First we need to understand for how long the battery can work. We can do that by dividing the total distance traveled by the speed of the race car. Since we do have both measurements required we can find the time. And so we get......

Now in order to find distance traveled by an object we need to multiply its speed by the time it traveled. Now since we have both of this measurements  we can fin the traveling distance.  We do ......

x =

And just like this we get the answer 75km

there are no contact forces mentioned on the list of choices that you've provided.