In the system of two blocks and a spring shown above, blocks 1 and 2 are connected by a string that passes over a pulley. The initially unstretched spring connects block 1 to a rigid wall. Block 1 is released from rest, initially slides to the right, and is eventually brought to rest by the spring and by friction on the horizontal surface. -4. After block 1 comes to rest, the force exerted on it by the spring must be equal in magnitude to (A) zero (B) the frictional force on block 1 (C) the vector sum of the forces on block 1 due to friction and tension in the string (D) the sum of the weights of the two blocks (E) the difference in the weights of the two blocks = E- 0 X Black 1 k 10000000 oooo 017 mg AT Block T - F = ma - Mz9 - F = ma