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# Physics day3

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PSHS 3rd Year Physics
Batch 2013
8 Exercises on Forces
Free body diagrams

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### Physics day3

1. 1. PHYSICS DAY 3<br />PSHS 3RD YEAR<br />
2. 2. SIGNIFICANT FIGURES<br />Recall DIAGNOSTIC TEST:<br /> Express the following sum with the correct significant figures: <br />Convert all measurements to the same unit: meter. Then transform to scientific notation. <br />
3. 3. Even as we changed the units, the measurements still resulted with the same number of significant figures. WHY?<br />ADDITION: <br />Least no. of decimal places = 2<br />3.759  3.76 m<br />
4. 4. Newton’s Laws<br />Example 1 (page 77, Giancoli)<br />FORCE TO STOP A CAR<br />What average net force is required to bring a 1500-kg car to rest from a speed of 100km/h within a distance of 55m?<br />
5. 5. Newton’s Laws<br />Example 2 (page 80, Giancoli)<br />A massive truck collides head-on with a small sports car. <br />a.) Which vehicle experiences the greater force of impact?<br />b.) Which experiences the greater acceleration?<br />c.) Which of Newton’s laws is useful to obtain the answers in (a) and (b)? <br />
6. 6. Motion<br />Motion<br />Motion<br />A<br />B<br />C<br />Example 3 (page 85, Giancoli)<br />A hockey puck is sliding at constant velocity across a flat horizontal ice surface that is assumed to be frictionless. Which of the sketches above is the correct free-body diagram for this puck?<br />
7. 7. Example 4 (page 89, Giancoli)<br />(Illustration not accurate)<br />A mover is trying to lift a piano (slowly) with a constant speed up to a second-story apartment. He is using a rope looped over two pulleys as shown. What force must he exert on the rope to slowly lift the piano’s 2000-N weight?<br />
8. 8. Push or pull a sled?<br />Example 5<br />Your younger sibling wants a ride on a wagon. If you are on flat ground, will you exert less force if you push or pull your sibling? Assume the same angle in each case.<br />
9. 9. Example 6 (page 103, Giancoli)<br />A block (mass m1) lying on a frictionless inclined plane is connected to a mass m2 by a massless cord passing over a pulley. <br />a.) Determine a formula for the acceleration of the system of the two blocks in terms of m1,m2, the angle theta and g.<br />
10. 10. A box weighing 77.0 N rests on a table. A rope tied to the box runs vertically upward over a pulley and a weight is hung from the other end. Determine the force that the table exerts on the box if the weight hanging on the other side of the pulley weighs<br />a.) 30.0 N<br />b.) 60.0 N<br />c.) 90.0 N<br />
11. 11. One 3.2-kg bucket is hanging by a massless cord from another 3.2-kg bucket, also hanging by a massless cord.<br />a.) If the buckets are at rest, what is the tension in each cord?<br />b.) If the two buckets are pulled upward with an acceleration of 1.60 m/s2 by the upper cord, calculate the tension in each cord.<br />