9 Tension Force (FT)Tension forces exist in cables, ropes, wires, strings, etc. The tension force pulls on an object where the direction of the tension is always away from the surface of the object to which the ‘rope’ is attached.mFTm
13 Example1A Mazda Miata has a mass of 1080kg and can go from zero to 26.8m/s (0 to 60 mph) in 7.9s. What magnitude of net force acts on the car?
14 Example 2A crane lowers a cable with a 1306kg car with an acceleration of 0.73 m/s2. The car starts 20.0m above the ground with an initial speed of zero.a) What is the tension in the cable?b) How much time will it take the car to reach the ground?
15 Example 3A person stands on a bathroom scale in an elevator at rest on the ground floor of a building. The scale reads 836N. As the elevator begins to move upward, the scale reading briefly increases to 935N but then returns to 836N after reaching a constant speed. a) Determine the acceleration of the elevator.b) If the elevator was moving at 3.0m/s upwards and then uniformly decelerated to rest in 4.7s, determine the scale reading.
16 Example4A 35.0 kg lawn mower is pushed across a level lawn in a direction of 0.0. The force exerted on the handle is . Assume friction is negligible.Determine the acceleration of the mower.Determine the normal force acting on the lawn mower.
17 Bird in a boxA bird sits on a sensitive scale inside a large cardboard box.
18 Falling appleForce of gravity is the action force for a falling apple.True or False: The Earth accelerates towards apple as apple falls towards ground.
19 EquilibriumObject is in equilibrium or is balanced when ΣF=0 in a particular direction.Determine the weight of the hanging picture.
20 Force of Friction (Ff)On a microscopic scale, most surfaces are rough.Two Types of Friction:1) Static Friction (Ffs)2) Kinetic Friction (Ffk )Force of friction tends to oppose the motion of objects
21 Friction depends on two things: 1) The normal force2) The coefficient of friction (μ)
22 In the case of static friction, there is a maximum value at which the static friction force will resist motion between surfaces.This means that if you push a table with 50N of force where maximum static friction is 75N, the table won’t break free. You need to push with just a smidge over 75N.
23 The static frictional force increases as the applied force increases, until it reaches its maximum.
24 Example1What minimum amount of force is needed to start to make a 250N crate move across a floor if the coefficient of static friction is 0.65?
25 Example2A traveler pulls a suitcase of mass 8.00kg across a level surface by pulling on the handle with 20.0N at an angle of 50.0° relative to horizontal. Coefficient of kinetic friction against the suitcase is μk =Determine the acceleration of the suitcase.
26 Example3A physics book is sent sliding across a lab table with a speed of 4.3m/s. If it takes the book 1.6m to stop, determine the value of the coefficient of kinetic friction.
27 Terminal VelocityConsider a skydiver who steps off a hovering helicopter at high altitude. NOW consider the effect of air resistance (friction) during the fall.Initially at t=0, what forces act on the skydiver?Initially at t=0, what is the acceleration and velocity of the skydiver?As the skydiver begins to fall, what happens to the force of air resistance on skydiver?As the skydiver continues to fall, describe what happens to their speed and acceleration? Why?Eventually what happens to the speed of the skydiver?
29 System of Bodies:Multiple bodies connected together is called a system where all bodies MUST accelerate at the same value.
30 Assume mA = 1kg, mB = 3kg, mC = 4kg and the surface on which they sit to be smooth. If block C is pulled with a force F equal to 15N, determine:a) The acceleration of the system.b) The tension in each string btw A & B and btw B & C.
31 Example2Block m2 (5.0kg) sits on rough surface where us= Determine the minimum value of m1 to accelerate the system. Assume a frictionless & negligible mass pulley.If m1 = 6.0kg, determine the tension in the string if uk = 0.30.
32 Example3Assume a frictionless & negligible mass pulley. If the system is released from rest, determine the speed of the 5kg mass after it has fallen for 1.3s.b) Determine the tension in the string.
33 Inclines θ Consider a block that slides down a frictionless incline. y xθSince the surface of the incline does not lie along x or y, we rotate our x-y axis to meet our needs.Draw the force of gravity vector
34 Example A skier moves down a ski slope angled at 30o. If the length of the slope is 50m, determine the time it takes to reach the bottom if the skier starts from rest. Ignore friction.
35 Example 2A block of mass 2kg is projected up a rough incline (uk = 0.40) at 6.2m/s where the angle of the incline is 25o.a) Determine the distance along the incline it slides before coming to rest.b) Determine the acceleration of the block on the way down the incline.
36 Example 3Determine the minimum value of m1 if us = 0.70,θ = 30o, and m2 = 3.0kg so that the system will start to accelerate when m1 is released.If m1 is 4kg, determine the tension in the string if uk = 0.35.