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Science Starter !

Science Starter !. A 1200 kg car is traveling along an icy road. Suddenly, the breaks fail! Because of friction, the car slows down at a rate of 0.98 m/s 2 . (a) Draw a free-body diagram of the car. Write an “ F Net Equation” for the vertical and horizontal directions.

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Science Starter !

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  1. Science Starter! A 1200 kg car is traveling along an icy road. Suddenly, the breaks fail! Because of friction, the car slows down at a rate of 0.98 m/s2. (a) Draw a free-body diagram of the car. • Write an “FNet Equation” for the vertical and horizontal directions. • Determine the force of friction between the car and the road. (d) If the car was originally traveling at 30 m/s, how far will the car travel before coming to a stop?

  2. Friction – Section 5.2

  3. Frictional Force Static Friction: friction that exists between two surfaces that are touching but NOT MOVING. (applied force > static friction to cause motion) Kinetic Friction: friction that exists between two surfaces that are moving against each other

  4. Equation Ff = μFN μ = coefficient of friction (depends on the material and has no units) FN = Normal Force Two different situations (still or moving?) μs = coefficient of static friction μk = coefficient of kinetic friction

  5. Example 1 A 20 kg cart is pushed with 25 N of force along a rough surface where μ = 0.10. • Draw a free-body diagram of the cart. • Write a “FNET Equation” in the horizontal and vertical directions. • Determine the acceleration of the cart.

  6. b) FNETy = FN – Fg FNETx = F – Ff c) may = FN – Fg max = F – μFN (20)(0) = FN– (20)(9.8) (20)(a) = 25 – (0.1)(196) 0 = FN – 196 (20)(a) = 25 – 19.6 FN = 196 N a = 0.27 m/s2

  7. Quiz You help your mom move a 41 kg bookcase to a different place in the living room. If you push with a force of 65 N, and the coefficient of friction between the carpet and the bookcase is 0.15, • Draw a free-body diagram of the bookcase. • Write a “FNET Equation” in the horizontal and vertical directions. • Determine the acceleration of the bookcase.

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