University:
Jackson College
Course:
PHY 231 | College Physics I
Academic year:

2024
Views:

68

Pages:

81
Author:

Crocirsp1

Lesson 1 DYNAMICS Definitions 1. Balanced Forces: sum of all forces = O. Therefore, there is either: NO MOTION or UNIFORM MOTION. When forces are BALANCED there is NO ACCELERATION. (a = 0) 2. Unbalanced Forces: sum of forces #O Therefore, there is an UNBALANCED FORCE AND an ACCELERATION. ΣF = ma This means there is an external unbalanced force and if there is an unbalanced "F" there is always an "a (and vice versa) doing 3. Inertia: the tendency of an object to keep doing what it is i.e. moving stay moving (eg. It is hard to stop a moving car) resting→ stay resting (eg. It is hard to move a parked bus) 4. Mass: the amount of matter in an object, which does NOT change with changing gravitational pull. Mass is measured in kg and is a way of measuring inertia (↑mass, ↑ inertia) Physics20. Dynamics. Newton2.Nordheimer 5. Weight: measured in Newtons (IN = 1 kg m/s²) Weight is measure of the gravitational pull on an object which changes with changing gravitational pull or ag. Weight is the SAME thing as force of gravity or F ↓ ↓ W = F= mag ↓ • a= -9.80 m/s² at earth's surface weight (N) force of mass gravity (kg) acceleration due to gravity (N) (m/s²) 9 6. Normal Force: when an object is placed on a surface, the object pushes down on surface, the object pushes down on the surface with its weight (F) and the surface pushes back with a force (FN or NORMAL FORCE). The FN is ALWAYS perpendicular to the surface and is used to calculate the force of friction: Fµ FN 7. Free Body Diagrams (FBD) show all the forces acting on one object a. stationary object FN T P Fg b. moving object FN Fapplied FF P 8. Newton's 3 Laws: 1st Law INERTIA 2nd Law F = ma 3rd Law for every action there is an equal and opposite reaction 2 Physics20.Dynamics, Newton2.Nordheimer lb Lesson 3 (continued The period of an object oscillating on a spring is where m is the mass of the object and kis the spring constant which indicates the force necessary to pro duce a unit elongation of the spring. The period of a simple pendulum is a. What mass will produce a 1.0-s period of oscil lation if it is attached to a spring with a spring constant of 4.0 N/m² b. What length pendulum will produce a period of 1.0 st c. How would the harmonic oscillator and the pen dulum have to be modified in order to produce 1.0-s periods on the surface of the moon where gis 1.6 m/s²? Chapter 8 (29 694) 1. Comet Halley returns every 76 years. Find the aver age distance of the comet from the sun. 2. Area is measured in m³, so the rate at which area is swept out by a planet or satellite is measured in m²/s. a. How fast is area swept out by Earth in its orbit about the sun? See table 8-1. b. How fast is area swept out by the moon in its orbit about Earth? Use 3.9 x 10 m as the average distance between the Earth and the moon, and 27.3 days as the moon's period. 3. You wish to launch a satellite that will remain above the same spot on Earthi's surface. This means the satellite must have a period of exactly one day. Cal culate the radius of the circular orbit this satellite must have. Hint: The moon also circles Earth and both the moon and the satellite will obey Kepler's third law. The moon is 3.8 x 10 m from Earth and its period is 27.33 days. 4. The mass of an electron is 9.1 x 10-31 kg. The mass of a proton is 1.7 x 10-2 kg. They are about 1.0 x 10-10 m apart in a hydrogen atom. What gravitational force exists between the proton and the electron of a hydrogen atom? (1.0NDN) 3. Two 1.00-kg masses have their centres 1.00 m apart. What is the force of attraction between them? (6.67x10W) 6. Two satellites of equal mass are put into orbit 30 m 10 N apart. The gravitational force between them is 2.0 x What is the mass of each satellite? (1.6x10kg) What is the initial acceleration given to each sat ellite by the gravitational force? Two large spheres are suspended close to each other. Their centres are 4.0 m apart. One sphere weighs 9.8 x 102 N. The other sphere has a weight of 1.96 x 10 N. What is the gravitational force between them? (8.3x10N) 8. If the centres of Earth and the moon are 3.9 x 10 m apart, the gravitational force between them is about 1.9 x 1020 N. What is the approximate mass of the moon? 9. a. What is the gravitational force between two spherical 8.00-kg masses that are 5.0 m aparti b. What is the gravitational force between them when they are 5.0 x 10 m apart? 10. A satellite is placed in a circular orbit with a radius of 1.0 x 10 m a period of 9.9 x 10 s. Calculate the mass of Earth. Hint: Gravity supplies the needed centripetal force for such a satellite. Scientists have actually measured the mass of Earth this way. 11. If you weigh 637 N on Earth's surface, how much would you weigh on the planet Mars? (Mars has a mass of 6.37 x 102 kg and a radius of 3,43 x 10 m.) 12. Using Newton's variation of Kepler's third law and Information from Table 8-1, calculate the period of Earth's moon if the radius of orbit was twice the ac- tual value of 3.9 x 10 m. 13. Use the data from Table 8-1 to find the speed and period of a satellite that would orbit Mars 175 km above its surface. 14. What would be the value of g, acceleration of grav- ity, If Earth's mass was double its actual value, but its radius remained the same? If the radius was dou- bled, but the mass remained the same? If both the mass and radius were doubled? 15. What would be the strength of Earth's gravitational field at a point where an 80.0-kg astronaut would experience a 25% reduction in weight? 16. On the surface of the moon, a 91.0-kg physics teacher weighs only 145.6 N. What is the value of the moon's gravitational field at its surfacel Physics 11-Newton's Third Law 1. While standing on a horizontal frictionless surface, two students push against each other. One student has a mass of 35 kg and the other 45 kg. If acceleration of the 35 kg student is 0.75 m/s², what is the acceleration of the other student? 2. While traveling 50 m/s, the rocket boosters are fired. The 1200 kg rocket pushes against the gas with an average force of 1500N back for 0.220 s. Calculate the velocity of the rocket at 0.115 s. force on rocket 3. TRUE or FALSE: As you sit in your seat in the physics classroom, the Earth pulls down upon your body with a gravitational force; the reaction force is the chair pushing upwards on your body with an equal magnitude. If False, correct the answer. 4. Shirley sits in her seat in her Engilsh classroom. The Earth pulls down on Shirley's body with a gravitational force of 600N. Describe the reaction force of the force of gravity acting upon Shirley. 5. Use Newton's third law (law of action-reaction) and Newton's second law (law of acceleration: a = F/m) to complete the following statements by filling in the blanks A bullet is loaded in a rifle and the trigger is pulled. The force experienced by the bullet is (less than, equal to, greater than) the force experienced by the rifle. The resulting acceleration of the bullet is (less than, equal to, greater than) the resulting acceleration of the rifle. b. A bug crashes into a high speed bus. The force experienced by the bug is, (less than, equal to, greater than) the force experienced by the bus. The resulting acceleration of the bug is (less than, equal to, greater than) the resulting acceleration of the bus. A massive linebacker collides with a smaller halfback at midfield. The force experienced by the linebacker is (less than, equal to, greater than) the force experienced by the halfback. The resulting acceleration of the linebacker is acceleration of the halfback. (less than, equal to, greater than) the resulting d. A 10-ball collides with the 14-ball on the billiards table (assuming equal mass balls). The force experienced by the 10-ball is (less than, equal to, greater than) the force experienced by the 14-ball. The resulting acceleration of the 10-ball is. acceleration of the 14-ball. (less than, equal to, greater than) the resulting Concept-Development Practice Page 6-1 Newton's Third Law 1. In the example below, the action-reaction pair is shown by the arrows (vectors), and the action-reaction described in words. In (a) through (d) draw the other arrow (vector) and state the reaction to the given action. Then make up your own example in (h). Example: Fist hits wall. Wall hits fist. Head bumps ball (a) Windshield hits bug (b) Bat hits ball. (c). Hand touches nose (d) Hand pulls on flower. (e) Athlete pushes bar upward. Compressed air pushes balloon surface outward (1) (g) 2. Draw arrows to show the chain reaction of at least 6 pairs of action-reaction forces below. YOU CAN'T TOUCH WITHOUT BENS TOUCHED NEWTOWNED LAW

Dynamics

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