I nd Hel Please? Which type of friction prevents a pile of rocks from falling apart?

rolling friction

static friction

cohesive friction

kinetic friction

Agymnast dismounts off the uneven bars in a tuck position with a radius of 0.3m (assume she is a solid sphere) and an angular velocity of 2rev/s. during the dismount she stretches out into the straight position, with a length of 1.5m, (assume she is a uniform rod through the center) for her landing. the gymnast has a mass of 50kg. what is her angular velocity in the straight position?

Anybody wanna ? (picture included? )

Which of these metals are magnetic?