Math 150B, Jagodina Ch 7.5-7.6 Packet Tutors may help. 1 7.5 Force and WorkForce is used to push or pull an object. To hold a 10 pound object takes 10 pounds of force since we are fighting the force of gravity. To move the object against the force requires work. To lift a 10 pound object 2 feet takes 10(2)=20 foot-pounds of work. Work=Force x Distance Work Units: foot-pounds, mile-tons, etc. Variable Force Often, a force is not constant. For example, to keep stretching a spring requires more and more force. Suppose a force is moving along a line from ato bGraph: So Work=11)lim)((()bkkkkannkknWf xf xxxf x dxHooke’s LawThe force F required to compress or stretch a spring (within its elastic limits) is proportional to the distance d that the spring is compressed or stretched from its original length. That is: natural lengthnatural length( )baFkdWoFrkx dxExample 1: A force of 9 pounds is required to stretch a spring from its natural length of 6 inches to a length of 8 inches. Find the work done in stretching the spring: a)From its natural length to a length of 10 inches b)From a length of 7 inches to a length of 9 inches .