t=At Identical blocks 1 and 2 slide on a horizontal surface toward a stationary barrierr At time t. = 0, block 1 collides with the barrier and slides backward. The blocks collide at time t 2 At. Assuming friction between the blocks and the horizontal surface to be negligible, which of the following statements is true about the two blocks? If the collision between block 1 and the wall is elastic, and the two blocks have an elastic collision, then (A) the sum of the kinetic energy of blocks 1 and 2 before block 1 makes contact with the wall will be equal to the sum of the kinetic energy of blocks 1 and 2 after the collision between the blocks. If the collision between block 1 and the wall is elastic, and the two blocks have an inelastic collision, (B) then the sum of the kinetic energy of blocks 1 and 2 before block 1 makes contact with the wall will be equal to the sum of the kinetic energy of blocks 1 and 2 after the collision between the blocks. If the collision between block 1 and the wall is not elastic, and the two blocks have an inelastic collision, (C) then the sum of the kinetic energy of blocks 1 and 2 before block 1 makes contact with the wall will be less than the sum of the kinetic energy of blocks 1 and 2 after the collision between the blocks If the collision between block 1 and the wall is not elastic, and the two blocks have an inelastic collision, (D) then the momentum of block 1 before it makes contact with the wall will be equal to the stun of the momenta of the two blocks after the collision between the blocks. If the collision between block 1 and the wall is not elastic, and the two blocks have an inelastic collision, (E) then the momennirn ofblock 1 before it makes contact with the wall will be equal to the sum of the momenta of the two blocks alter the collision between the blocks. 2. Block 1 BIOC" 2 m Block 1 of mass m is moving with speed 'U to the right on a horizontal surfacc ofnegligiblc friction, as shown in the gure. Block 1 makes an elastic, head-on collision with block 2 of mass 2m, which is at rest. Which of the following are correct velocities in and 'tJ'2 for blocks 1 and 2, respectively, immediately aer the collision? AP Physics C: Mechanics Page 1 of 22 m Scoring Guide Unit 4.3 Conservation of Momentum and Collisions _ 1 _ 2 (A) 1;] _ 31) and U2 Ell ' (B) v1=%Ua.ndv2=%v V/ {land in 2 $1) 1 1 v and v2 : 3v _ 1 _ 1 (E) U] _ it) and v2 it) (C) U1 (D) \"\"1 6. When the truck and car stuck together after the collision, the speed of the center of mass of the truck-car system is Vf. If the truck and car have an elastic collision, the speed of the center of mass of the truck-car system is V/2. Which of the following expressions for Vy2 must be true? (A) V/2 > 2V; (B) VJ