dnd 5e – How can players take impossible actions together?

By RAW, you are right

You have already quoted the relevant rule. If a character does not have the strength to lift / slide the rock (see Lifting and Carrying, PHB p.176), it is impossible for them to move, and this falls into the "questionable" category. to be able to attempt the action, at best.

But clearly it does not make any sense

Lifting or pushing a large object in tandem with others is the ideal poster for tasks that benefit multiple participants (provided there is room for everyone).

You (assuming that you are the SM in this scenario, if you are not, propose it there) would have quite your right to decide that anything that has a Strength score would be able to & # 39; 39, use the Help action to contribute to their excess Lift. / Drag the ability to the task.

Technically, it would not even require a check to lift it (the clutter works like a passive force score, all you have to do is add the total and compare it to the size of the block).

Effectively, your players would create an improvised trap Rolling Sphere, to which we can borrow mechanisms:

… a solid stone sphere rolling 10 feet in diameter … moves in a straight line over 60 feet. [It] can move in spaces of creatures, and creatures can move in its space, treating it like a difficult terrain.

Whenever the sphere enters the space of a creature or a creature enters its space while it rolls, this creature must succeed in saving DC dexterity. 15 or suffer 55 (10d10) blunt blows and be knocked out.

… As an action, a creature within 5 feet of the sphere may attempt to slow it down with a DC 20 Strength test. When successfully controlled, the sphere's speed is reduced by 15 feet. If the speed of the sphere drops to 0, it stops moving and no longer represents a threat.

[DMG p.123]