PHYSICS DAY 3PSHS 3RD YEAR

SIGNIFICANT FIGURES

Recall DIAGNOSTIC TEST:Express the following

sum with the correct significant figures:

51.80 142.5 5.34 10m cm m Convert all measurements to the same unit: meter. Then transform to scientific notation.

1.80m 1.425m 1 5.34 10 m

Even as we changed the units, the measurements still resulted with the same number of significant figures. WHY?

11.80 1.425 5.34 10m m m

ADDITION: Least no. of decimal places = 2 1.80

1.425 0.534

3.759

3.759 3.76 m

Newton’s Laws

Example 1 (page 77, Giancoli)FORCE TO STOP A CARWhat average net force is required to

bring a 1500-kg car to rest from a speed of 100km/h within a distance of 55m?

Newton’s LawsExample 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)?

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?

Motion Motion Motion

A B C

GF

GF

GF

NF

NF

NF

F

F

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?

Push or pull a sled?

Example 5Your 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.

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.

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 weighsa.) 30.0 Nb.) 60.0 Nc.) 90.0 N

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.