WORKENERGY PRINCIPLE The work of a resultant external

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WORK-ENERGY PRINCIPLE: The work of a resultant external force on a body is equal

WORK-ENERGY PRINCIPLE: The work of a resultant external force on a body is equal to the change in kinetic energy of the body. W= K Units: Joules (J)

Work Energy Theorem – Proof! A net force acts on a moving object v

Work Energy Theorem – Proof! A net force acts on a moving object v vo F m x Kinetic Energy

What average force F is necessary to stop a 16 g bullet traveling at

What average force F is necessary to stop a 16 g bullet traveling at 260 m/s as it penetrates into wood at a distance of 12 cm? m = 0. 016 kg r = 0. 12 m vo = 260 m/s vf = 0 m/s W = ΔK = - 4506. 7 N

Work Done by a Constant Force Friction acts on moving object m m f

Work Done by a Constant Force Friction acts on moving object m m f d • If the net work is positive, the kinetic energy increases. • If the net work is negative, the kinetic energy decreases.

You are pulling 100 kg crate by a rope at 40° for 15 m

You are pulling 100 kg crate by a rope at 40° for 15 m across a surface with friction. What is the net Work done on the box if it was initially sliding at 1 m/s and ended up with a speed of 3 m/s? A. 400 J B. 200 J C. 150 J D. 10 J E. Can’t be determined

You are pulling 100 kg crate that was initially moving at 1 m/s by

You are pulling 100 kg crate that was initially moving at 1 m/s by a rope at 40° for 15 m across a surface with friction, causing it to now have a speed of 3 m/s. Is it possible to determine the Work done by Tension on the box with the given information? A. Yes B. No

You are pulling 100 kg crate by a rope at 40° for 15 m.

You are pulling 100 kg crate by a rope at 40° for 15 m. What would cause the net Work done on the box to be negative if it was initially sliding at 1 m/s? A. fk > FTx B. If the crate slowed down C. Both of A & B D. Net Work can’t be negative b/c it doesn’t have direction

A child starts at rest at the top of a slide and slides down

A child starts at rest at the top of a slide and slides down going pretty fast at the bottom. What are the signs of the Work done by individual forces, the Net Work, and Change in Kinetic Energy during that process? W fk W Fg W FN Wnet ΔKE A. + + + B. – + 0 + + C. – – 0 + + D. – + 0 – + E. – – + F. None of these

Work done by gravity Object falls in a gravitational field Work and Energy m

Work done by gravity Object falls in a gravitational field Work and Energy m Work done by force (F) = mg h m Wg = mgh Kinetic energy = Work done by gravity = Work done against friction =

Can you solve #13 by: a) Work energy theorem b) Conservation of energy c)

Can you solve #13 by: a) Work energy theorem b) Conservation of energy c) kinematics

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