Instruction: Answer the following. Show all your solutions. 4. A spring has a natural length of 10 in., and a 30-lb force stretches it to 11} in. Find the work done in stretching the spring from 10 in. to 12 in. . 5. A trough full of water is 20ft. long and its cross section is in the shape of an isosceles triangle 4ft. wide across the top and 4ft. deep. How much is the work done in pumping all the water out of the trough over the top? ( 6. The face of the gate of a dam is in the shape of an isosceles trapezoid 3 ft. wide at the top, 4 ft. wide at the 4/6 bottom, and 3 ft. high. If the upper base is 20 ft. below the surface of the water, find the total force due to liquid pressure on the gate. "