The force of the ruler on the ball is called an applied force. The force of the barrier on the ball is called a normal force. Both of these forces are exerted by surfaces, and the direction of force is at a right angle to the surface. The difference is that an applied force is exerted by a moving object and a normal force is exerted by a stationary object. Draw two arrows to represent the applied force and the normal force on the ball.

How many electrons in an atom could have these sets of quantum numbers? =3n=3 electronselectrons =4,ℓ=2n=4,ℓ=2 electronselectrons =6,ℓ=ℓ=−1n=6,ℓ=2,mℓ=−1

Atruck going 15 kmôź°€h has a head-on collision with a small car going 30 kmôź°€h. which statement best describes the situation? (a) the truck has the greater change of momentum because it has the greater mass. (b) the car has the greater change of momentum because it has the greater speed. (c) neither the car nor the truck changes its momentum in the collision because momentum is conserved. (d) they both have the same change in magnitude of momentum because momentum is conserved. (e) none of the above is necessarily true. 2. a small boat coasts at constant speed under a bridge. a heavy sack of sand is dropped from the bridge onto the boat. the speed of the boat (a) increases. (b) decreases. (c) does not change. (d) without knowing the mass of the boat and the sand, we can’t tell.

Low areas cut into a gun barrel are called