Which is greater, the mass of the compounds before a chemical reaction or the mass of the compounds after a chemical reaction?

the mass of the compounds before is greater.
the mass of the compounds after is greater.
the masses before and after are equal.
it depends on the type of chemical reaction.

Acricket ball of 70g moving with a velocity of 0.5 m/s is stopped by a player in 0.5s what is the force applied to stop the ball

Aperson stands on a platform, initially at rest, that can rotate freely without friction. the moment of inertia of the person plus the platform is ip. the person holds a spinning bicycle wheel with its axis horizontal. the wheel has moment of inertia iw and angular velocity ωw. take the ωw direction counterclockwise when viewed from above. part a what will be the angular velocity ωp of the platform if the person moves the axis of the wheel so that it points vertically upward?

Acid rain is caused by human activity. select the best answer from the choices provided t f