PHY 1150

PHY 1151

Doug Davis

Ch 5, Newton's Laws of Motion

| ToC, Chapter 5 | Course Calendar |

D5.1 Shown in the figure are six rocks which have been thrown straight up. The rocks all have the same size and shape, but they have different masses. The rocks are all thrown straight up, but with different speeds. The masses of the rocks and their speeds when released are given in the figure. All start from the same height. Neglect air resistance. Rank these rocks on the basis of the maximum height attained.

mass:

v_i
A
1.0 kg

2.5 m/s
B
1.1 kg

2.3 m/s
C
1.3 kg

3.8 m/s
D
2.5 kg

2.5 m/s
E
2.8 kg

1.3 m/s
F
4.1 kg

2.7 m/s

D5.2 Shown in the figure are six laboratory carts of varying masses. Each has an initial velocity and a net force as shown in the figure. Rank these carts on the basis of their final velocity after 10 seconds.

D5.3 The acceleration of gravity on the Moon's surface is about one-eighth what it is on Earth's surface. What is the weight on the Moon of an astronaut whose mass is 85 kg?
D5.4 A block starts from rest and slides down a frictionless inclined plane that is inclined 20° from the horizontal and is 2.5 meters long. How fast is the block moving as it reaches the bottom?

D5.5 Four airline baggage carts are coupled as shown in the figure to make a "train"; each has a mass of 250 kg. Find the force F that must be applied to accelerate this "train" at 0.8 m/s². Find the tension in each of the three couplings between the baggage carts.

D5.6 A 50 ton (50,000 kg) rocket is acted on by an upward thrust of 600 kN. If the rocket is 25 m tall, how long does it require to rise off the launching pad a distance equal to its own height?

Always start with a good, clear, detailed free-body diagram:

D5.7 Two small balls of equal mass are connected by a string 1.0 m long and are laid out on a smooth (ie, frictionless) table with one ball (A) just at the edge of the table and the other ball (B) 1.0 m from the edge. The table is 0.5 m high. Ball A is nudged gently over the edge of the table, and things begin to happen.

a) How much time is required for ball A to strike the floor?
b) How much time is required for ball B to strike the floor?

c) How far from the base of the table does ball B strike the floor?

Good diagrams are always essential and that is certainly true for this situation.

D5.8 A 7-kg package sits on a rough but level floor. The coefficient of sliding friction between the package and the floor is 0.27. A cord is attached to the package and makes an angle of 30° above the horizontal. What must be the tension in the cord to move the package along the surface with an acceleration of 1.0 m/s²?

D5.9 A man pushes a 20-kg lawn mower at constant speed with a force of 80 N directed along the handle, which makes an angle of 37° with the horizontal. Calculate the following:

a) the horizontal and vertical components of the man's force.
b) the horizontal retarding force on the mower.

c) the normal force between the mower and the lawn (be sure to include the mower's weight).

d) the effective coefficient of friction in this case.

| ToC, Chapter 5 | Course Calendar |