Physics – 4.2 Equilibrium WS Name_________________________ Hour_____ 1. Suggest you are pushing a shopping cart across a paved parking lot at 40 N to the right. If the cart is in equilibrium, how much frictional force is present and it what direction is this force? (40 N Left) 2. Three little children are in a tug of war against a grown man. The man decides he is going to just provide enough force to keep the rope from moving. If the children pull to left at 30N, 52 N and 61 N, how much force does the man have to exert to keep the rope stationary? (143 N in opp dir) 3. A 15 foot tree has to be replanted into a new location. To make sure it does not get blown over by the wind, three ropes are attached to the trunk and staked into the ground. The first rope pulls the tree at 41 N to the East. The second rope pull the tree at 67 N to the South. In what direction should the third rope be positioned to put the tree’s trunk in “equilibrium”? ( ° W of N) 4. A kite that has been flying for several minutes is stationary in the air for a few seconds. During this time of equilibrium, what is the magnitude of the tension (force) in the string if the weight of the kite is 13 N, the wind exerts a force of 52 N at an angle of 54° above the horizon? (42 47 ° W of S) 5. Before running to the playground, an elementary student sets his 40 N book bag down on a concrete, handicap access ramp. The ramp has an incline of 10° and the book bag does not move because of friction. What is the frictional force? (7 N up the ramp) 6. An usher is wheeling around a 300 N cart with refreshments at a Utica Play in the Auditorium. He is pushing the cart from the front row towards the back of auditorium. Notice he is pushing the cart up an incline (the incline is only 5°). There is enough friction so that when he lets go of the cart, it does not roll down the incline. How much frictional force is present? (26 N up the ramp) 7. A traffic light is suspended over an intersection as in the picture to the right. How much tension (force) will be in the unknown cable, and in what direction? (561 42° N of E) 8. A three way tug of war is going on between the sophomores, juniors and seniors. The seniors are by far the stronger team, so they decide that for the first 30 seconds of the contest that they will provide the necessary force to keep the rope in equilibrium and then they will start to crush. Using the picture to the right, how much force (magnitude) will they have to pull with? What is the direction of this force? (find θ) ( ° W of S) 9. As a field engineer for Sprint, you are tasked with securing a large antenna to the top of a building in Manhattan. The building code states you must secure the antenna with four cables. Three cables have already been installed (see pic). How much tension (force) must be applied in the fourth cable so that the cables put the antenna in “equilibrium”? (526 14° E of N) Do this on a separate sheet 90° West 30° 1600 N 1360 N 1700 N 30° Sophomores 2200 N Juniors 2900 N Seniors ? N θ θ 90° South East 420 N 372 N ? N