LG .1 Work

• Force 


  What is needed to displace or move an object?
• Work


  Quantifies the amount of energy transfer that occurs when an object.
• What if the man exerts a GREATER FORCE?

  Energy is INCREASED
• What if the force is applied over a GREATER DISPLACEMENT?

  Energy is INCREASED
• What happens to the force when component points in the ​SAME direction as the displacement vector?

  Force is POSITIVE
• What happens to the force when component points in the OPPOSITE direction as the displacement vector?

  Force is NEGATIVE
• What happens to the force when component is PERPENDICULAR to the displacement?

  Force is ZERO
• What is the work done by the person on the grocery bag while he carries it across the room as shown in the figure?

  Work is ZERO

  Force exerted by the person is UPWARD

  Displacement of the grocery is HORIZONTAL

  
• What is the unit of work?

  Joules (J)
• Given formula W=Fd:

  If you push a cart with a force of 60 N for 2 m, how much work have you done?

  120 J
• Fred kicks a ball with a force of 20N to George, who is 5M away. How much work was done to the ball?

  100 J
• If 40N of force is applied to Rollo Koster's 10 kg cart over a distance of 50 meters, how much work is done?

  2000 J
• If something is shifted a long way then there MORE work is being done
• Working alone at a constant rate, Carla can wash a load of dishes in 42 minutes. If Carla works together with Dan and they both work at constant rates, it takes them 28 minutes to wash the same load of dishes. Working at a constant rate, how long would it take Dan to wash the load of dishes by himself?

  84 Minutes
• Working alone, it takes Asanji eight hours to dig a 10 ft by 10 ft hole. Brenda can dig the same hole in nine hours. How long would it take them if they worked together?

  4 Hours
• It takes Kali eight minutes to sweep a porch. Shawna can sweep the same porch in 11 minutes. If they worked together how long would it take them?

  5 Minutes
• Sally and Dan were able to paint a room in 3 hours together. It takes Dan 4 hours to do this job alone. Without help, how long would it take Sally to do this job ?

  12 Hours
• A man reels in what he thinks is a fish. He estimates it has a mass of 3 kg. He starts reeling at a rate of 5 m/s2. He thinks his line is out 7 meters.

  Force: ​ (a)  

  Work: (b)  

  (a) 12 N

  (b) 105 J
• Kinetic energy is energy in motion. It is a scalar quantity. Can be zero when the object is at rest but it can never be negative.
• What is the SI unit of Kinetic Energy?

  Joules (J)
• What happens to the speed if the work done is POSITIVE?

  Speed is INCREASED
• What happens to the speed if the work done is NEGATIVE?


  Speed is DECREASED
• What happens to the speed if the work done is ZERO?


  Speed is CONSTANT