Your problem, in reality, is a bit more technical than it looks at first glimpse.
It seems you need these specific requirements:
The exposure should reflect the velocity, so at point (1) it should look less bright because is passing faster, ant point (2) should be brighter, because it is moving slower, and you want to see the object clearly in (3) at the extremes.
Let us address point 1 and 2.
You do not want to use a single source of light at the center because you will have a hotspot at the center canceling the "speed" effect. This light will expose more at the center if it is either far enough or big enough. (Probably one big diffuse light can work)
What I recommend is that you exaggerate this speed effect using two lateral lights.
So the effect is more visible because you will have a bot more light when the pendulum is at the extremes.
But here is the real technical problem.
To expose exactly the object at the edges you probably need a light sensor trigger, probably an infrared one so this light does not add to the photo.
But you can overcome it in several ways.
Manually triggering a flash at the extremes (I then recommend a soft trigger, probably using remote triggers like Yongnuo 603 which is really cheap) because the built-in button on a flash, the test button usually is hard to press, for safety reasons)
I would not recommend a very long exposition for one reason, it probably can detect the decay of several passes, increasing exposure at the center. Of course, this decay depends on how massive is the pendulum.
Try to limit this exposition to 2-3 passes only, so do not use very dim lights.
Some lights can have a flicker effect, so take that into account.