Why is Elie whipped in Night?

Idek the Kapo rules the other prisoners with an iron fist. A brutal, sadistic man, he's prone to sudden outbursts of extreme violence. On one such occasion it's Elie who's on the receiving end. It's a Sunday, and Elie has been assigned to work in an electrical warehouse. Prisoners are not normally supposed to work on Sundays, so there's nothing for Elie or the other inmates to do.

Idek disappears, and a bored Elie decides to go for a walk. Out and about on his travels, he sees Idek with a girl. Elie bursts out with laughter at the sudden realization that he and the other men were taken to the warehouse just so Idek could be with a girl; however, Idek is not amused. He responds to Elie's laughter with yet another outburst of savage violence, beating Elie unconscious with a whip.

Why was Elie Wiesel beaten for the second time in Night?

In the haunting book, Night, by Elie Wiesel, Elie tells his personal story of the Holocaust. Conditions in the camps are inhumane and cruel, but Elie feels somewhat lucky to have been assigned to work at an electrical warehouse, where he is able to stay with his father. The Kapo, Idek, who is in charge of the warehouse, leaves the workers alone for the most part but is prone to having fits of anger once in awhile, and the prisoners quickly learn to stay out of his way. On a Sunday, when the men are not supposed to work, Idek takes them to the warehouse, and then he disappears. Elie, upon having nothing else to do, goes for a walk and discovers Idek with a girl. He bursts into laughter, realizing that they had all been made to go to the warehouse just so Idek could be with a girl. Of course, this enrages Idek, and later that day, Idek beats him with a whip so viciously, Elie passes out.