PSHS 3rd Year Physics Batch 2013 8 Exercises on Forces Free body diagrams * answers still to be uploaded :) Copyright: Young Einstein, www.yeinstein.com

1. PHYSICS DAY 3 PSHS 3RD YEAR

2. SIGNIFICANT FIGURES Recall DIAGNOSTIC TEST: Express the following sum with the correct significant figures: Convert all measurements to the same unit: meter. Then transform to scientific notation.

3. Even as we changed the units, the measurements still resulted with the same number of significant figures. WHY? ADDITION: Least no. of decimal places = 2 3.759  3.76 m

4. Newton’s Laws Example 1 (page 77, Giancoli) FORCE TO STOP A CAR 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?

5. Newton’s Laws Example 2 (page 80, Giancoli) A massive truck collides head-on with a small sports car. a.) Which vehicle experiences the greater force of impact? b.) Which experiences the greater acceleration? c.) Which of Newton’s laws is useful to obtain the answers in (a) and (b)?

6. Motion Motion Motion A B C Example 3 (page 85, Giancoli) 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?

7. Example 4 (page 89, Giancoli) (Illustration not accurate) 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?

8. Push or pull a sled? Example 5 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.

9. Example 6 (page 103, Giancoli) A block (mass m1) lying on a frictionless inclined plane is connected to a mass m2 by a massless cord passing over a pulley. a.) Determine a formula for the acceleration of the system of the two blocks in terms of m1,m2, the angle theta and g.

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 a.) 30.0 N b.) 60.0 N c.) 90.0 N

11. One 3.2-kg bucket is hanging by a massless cord from another 3.2-kg bucket, also hanging by a massless cord. a.) If the buckets are at rest, what is the tension in each cord? 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.