Warm-Up: December 11, 2015  A 1.75 kg rock is thrown north at a speed of 3.00 m/s. A ball of clay is thrown south at a speed of 2.00 m/s. The rock gets stuck in the clay and they move south together at a speed of 1.25 m/s. What is the mass of the clay?

Calculator Quiz Answers

Momentum and Impulse Worksheet

Conservation of Momentum worksheet

Questions about Momentum?

Work and Power Section 10.1

Work

Work and Dot Product

Example 1  A rope is pulling a box horizontally across a horizontal floor. If the tension of the rope is 125 N and the box moves 4.00 m, how much work was done?

You-Try #1  A man pushes his car horizontally 10.0 m down his driveway, pushing with a force of 250 N. The driveway is 2.00° from horizontal. How much work did the man do?

Example 2  A weightlifter lifts a barbell 0.70 m at a constant speed by exerting 140 J. What is the weight of the barbell?

You-Try #2  A woman pulls a refrigerator at an angle of 20.° above horizontal while exerting 250 J. The refrigerator moves 0.50 m across a horizontal floor. With what force did she pull?

Example 3  How far can you push a box with a force of 75 N without exceeding J?

You-Try #3  A mother goes for a walk while pushing a baby stroller with a force of 5.0 N, directed at a 45° angle relative to horizontal. If she does 275 J of work on the stroller, how far did she walk along the horizontal street?

Warm-Up:  A child pulls a blanket 2.2 m while exerting 11 J. With what force did the child pull?

Homework Questions?

Power

Example 4  A rope is pulling a box across a horizontal floor. The tension of the rope is 125 N and the rope is 15.0° above horizontal. The box moves 4.00 m. If it takes 20.0 s to move the box, how much power is used?

You-Try #4  A man horizontally pushes his car 10.0 m down his driveway, pushing with a force of 250 N. If the driveway is 2.00° from horizontal and the man takes 50.0 s to move his car, how much power did it take to move the car?

Example 5  A weightlifter lifts a barbell 0.70 m at a constant speed by exerting 140 J. If it takes 210 W to move the barbell, how many seconds did it take?

You-Try #5  A woman pulls a refrigerator at an angle of 20.° above horizontal while exerting 300. W and 250 J. How many seconds did it take to move the refrigerator?

Warm-Up: December 14, 2015  A rope is pulling a box up a 10.0° inclined ramp. The tension of the rope is 75.0 N and the box moves 3.00 m. The rope is parallel to the ramp. If it takes 15.0 s to move the box, how much power is used?

You-Try #6  If a person uses 750 W and 325 J horizontally pushing a box 7.70 m along a horizontal floor, what is the impulse that the person applies to the box?

Example 7  A box is pushed 14.9 m at a constant speed of 1.8 m/s. The box has a mass of 21 kg and the coefficient of kinetic friction between the box and the floor is Calculate: a) Force of gravity (weight) of the box b) Normal force c) Friction force d) Push force e) Work f) The time it takes to move the box g) Power

You-Try #7  A box is pushed 7.90 m at a constant speed of 3.30 m/s along a horizontal floor. The push force is directed 20.0° below horizontal. The box has a mass of 12.5 kg and the coefficient of kinetic friction between the box and the floor is Calculate: a) Force of gravity (weight) of the box b) Normal force c) Friction force d) Push force e) Work done moving the box f) The time it takes to move the box g) Power output while moving the box

Assignments  Work and Power worksheet  Read Chapter 10  Page 278 #52-57, 59