arrow shaft
笴 centers on the shaft of an arrow, the long straight part that connects the tip to the fletching.
笴 combines 竹 (bamboo) with 可, which likely contributes the sound. Bamboo was historically used for arrow shafts, so the character suggests a bamboo shaft.
The top 竹 is bamboo, and the bottom 可 looks like a shaft with a notch. Picture a bamboo stalk being straightened into an arrow shaft.
For カ, imagine a car (カ) driving straight like an arrow shaft: car -> カ, and the shaft flies true.