Why do we use a spaceship in outer space, far from other objects, to illustrate Newton's first law? Why not a car or a train? (More than one of the following statements may be correct.) (1) A car or train touches other objects, and interacts with them. (2) A car or train can't travel fast enough. (3) The spaceship has negligible interactions with other objects. (4) A car or train interacts gravitationally with the Earth. (5) A spaceship can never experience a gravitational force.
Correct statements are (1), (3) and (4).
According to Newton’s First Law of motion, if a body is at rest it will remain at rest or if a body is in motion it will remains in motion unless it is compelled by any external force.
Cars or trains are always in contact with roads or railway tracks. So, contact forces are present. Significant interaction is present between cars or trains and other objects. Therefore, cars or trains are not used to illustrate Newton’s first law. Hence the statement (1) is true.
It is true that cars or trains can’t travel fast enough compared to a spaceship. But speed is not a factor which is used to illustrate Newton’s first law. It is illustrated by the contact forces present between objects. So, speed of the body does not matter. Hence the statement (2) is false.
The spaceship is present in vacuum. There is no environment there. Hence, there is no interaction with other objects. So, Newton’s first law can be illustrated. Hence the statement (3) is true.
Cars or trains are under the gravitational pull of earth. Therefore, interaction is present between earth and these bodies. This is the reason Newton’s first law is generally not illustrated by these bodies. Hence the statement (4) is true.
A spaceship may experience gravitational force when it is close to a certain planet. It is not necessary that a spaceship can always be used to illustrate Newton’s first law due to this reason. Hence the statement (5) is false.
Thus, out of all, the true statements are (1), (3) and (4).
In the periodic table on the inside front cover of this book (or one you find on the internet), for each element there is given the "atomic number," the number of protons or electrons in an atom, and the "atomic mass," which is essentially the number of nucleons, protons plus neutrons, in the nucleus, averaged over the various isotopes of the element, which differ in the number of neutrons. Make a graph of the number of neutrons vs. the number of protons in the elements. You needn't graph every element, just enough to see the trend. What do you observe about the data? (This reflects the need for more neutrons in proton-rich nuclei in order to prevent the electric repulsion of the protons of each other from destroying the nucleus.)
(a) Powerful sports car can go from zero to 25m/s (about 60mi/h) in 5 s. (1) What is the magnitude of average acceleration? (2) How does this compare with the acceleration of a rock falling near the Earth’s surface? (b) Suppose the position of an object at time tis . (1) what is the instantaneous velocity at time t? (2) What is the instantaneous acceleration at time t? (3) What is the instantaneous velocity at time t=0? (4) What is the instantaneous acceleration at time t=0?
Here are the positions at three different times for a bee in flight (a bee’s top speed is about 7 m/s ). (a) Between 6.3 s and 6.8 s , what was the bee’s average velocity? Be careful with signs.
(b) Between 6.3 s and 7.3 s, what was the bee’s average velocity? Be careful with signs.
(c) Of the two average velocities you calculated, which is the best estimate of the bee’s instantaneous velocity at time 6.3 s ?
(d) Using the best information available, what was the displacement of the bee during the time interval from 6.3 s to 6.33 s ?
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