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# 1/12/12 PowerPoint PPT Presentation

1/12/12. What does it mean if the value of work is negative? Work, force, or displacement is backwards or down. A horizontal force of 300 N is applied to move a 45 kg television set across a 5.0 m level surface. What is the work done by the 300 N force on the television set? W = 1500 J.

1/12/12

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## 1/12/12

What does it mean if the value of work is negative?

Work, force, or displacement is backwards or down

A horizontal force of 300 N is applied to move a 45 kg television set across a 5.0 m level surface. What is the work done by the 300 N force on the television set?

W = 1500 J

What is the kinetic energy of a 0.235 kg baseball thrown at 30.0 m/s?

KE = 7.05 J

What are equations for power, P, in terms of work, W, displacement, d, time interval, t, force, F, and/or velocity, v?

P = w/t P = e/t P= Fd/t P = Fv

What is the unit for work?

W = Joules (J)

What is the unit for any type of Energy?

E = Joules (J)

What is the SI unit for power?

P = Watts (W)

What is the SI unit for momentum?

p = kg x m/s

What is the average power supplied by a 90.0 kg person running up a flight of stairs a vertical distance of 6.5 m in 8.2 s?

P = Fd/t = mgh/t = 700 W

A rubber ball moving at a speed of 5.6 m/s hit a flat wall and returned to the thrower at 5.6 m/s. The magnitude of the momentum of the rubber ball ____? What type of collision is this?

A 0.26 kg baseball is pitched with a velocity of 38 m/s and is then batted to the pitcher with a velocity of 58 m/s. What is the magnitude of change in the ball’s momentum?

p = 25 kg x m/s

Two objects with different masses collide and bounce back after an elastic collision. Before the collision, the two objects were moving at velocities equal in magnitude but opposite in direction. After the collision, describe the momentum changes in both objects.

A jet engine develops 5,000 N of thrust to move an airplane forward at a speed of 200 km/h. What is the power output of the engine?

P = 30,000 W or 30 kW

A player at first base catches a throw traveling 25 m/s. The baseball, which has a mass of 0.18 kg, comes to a complete stop in the glove after 0.40 s. Assuming the force of the glove was uniform, what force did the glove exert on the ball?

F = p/t = 11 N

An astronaut with a mass of 70 kg is outside a space capsule when the tether line breaks. To return to the capsule, the astronaut throws a 1kg wrench away from the capsule at a speed of 3 m/s. At what speed does the astronaut move toward the capsule?

p = p 70kg (v) = 3kg x m/s v = 0.04 m/s

A 80 kg halfback runs north and is tackled by a 90 kg opponent running south at 4 m/s. The collision is perfectly inelastic. Just after the tackle, both players move at a velocity of 0.5 m/s north. Calculate the velocity of the 80 kg player just before the tackle.

v = 3.4 = 3 m/s