Question: You drop a piece of paper, and observe that it eventually falls at a constant speed. Which of the following statements about this situation is based on a fundamental physics principle? (a) Because the paper is moving downward, we know that it experiences a nonzero net downward force. (b) Since the momentum of the paper does not change from one instant to the next,, and therefore the net force on the paper must be zero. (2) You give a push to a toy car, which rolls away smoothly on a wooden floor. Why does the car keep moving after your hand is no longer touching it? (a) The momentum of the car just after it leaves your hand reflects the total impulse given to the car by your hand. (b) Your hand continues to exert a force on the car even after the car and hand no longer touch.

Short Answer

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Answer

(1) (b) is the correct statement.

(2) (a) is the correct statement.

Step by step solution

01

Understanding Newton’s first law

Newton's first law asserts that if any particular body is at a rest position or moving in a straight path at a constant speed, it will remain at rest position or continue to move in the same straight line at a constant speed until acted upon by a particular force.

The interactions between particles and physical things are governed by the physical laws of matter, energy, and the fundamental forces of nature, according to physics.

02

(1) Using Newton’s first law in option (b)

The paper has a constant velocity which means it has a constant speed and constantly travels downhill.

The momentum is constant and does not vary. So, the net interaction of this paper with its surroundings is zero as per according to Newton's first law.

Thus, option (b) is the correct option.

03

Explanation for option (a)

Zero interaction of paper with its surroundings does not imply that there must be motion.

It implies that the object's status of motion will change as a result of the contact between the paper with its surroundings.

Thus, statement (a) is incorrect.

04

(2) Understanding the role of the momentum in option (a)

The momentum is maintained throughout the history of interactions between the automobile and its surroundings. So, the car keeps moving after the hand is no longer touching it.

Thus, the right statement isa

05

Explanation for option (b)

The hand no longer exerts force, and there is no contact between the hand and the automobile once the car has departed. The hand cannot continue to exert a force on the car even after the car and hand are no longer in touch.

Thus, statement is wrong.

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Most popular questions from this chapter

A tennis ball has a mass of 0.057kg.A professional tennis player hits the ball hard enough to give it a speed of 50 m/s (about 120 mi/h). The ball hits a wall and bounces back with almost the same speed (50m/s). As indicated in Figure 2.55 , high-speed photography shows that the ball is crushed 2 cm (0.02 m) at the instant when its speed is moment0arily zero, before rebounding.

Making the very rough approximation that the large force that the wall exerts on the ball is approximately constant during contact, determine the approximate magnitude of this force. Hint: Think about the approximate amount of time it takes for the ball to come momentarily to rest. (For comparison note that the gravitational force on the ball is quite small, only about (0.057 kg) (9.8 N/kg) 0.6 N. A force of5N is approximately the same as a force of one pound.)


Question: The following questions refer to the circuit shown in Figure 18.114, consisting of two flashlight batteries and two Nichrome wires of different lengths and different thicknesses as shown (corresponding roughly to your own thick and thin Nichrome wires).


The thin wire is 50 cm long, and its diameter is 0.25 mm. The thick wire is 15 cm long, and its diameter is 0.35 mm. (a) The emf of each flashlight battery is 1.5 V. Determine the steady-state electric field inside each Nichrome wire. Remember that in the steady state you must satisfy both the current node rule and energy conservation. These two principles give you two equations for the two unknown fields. (b) The electron mobility

in room-temperature Nichrome is about 7×10-5(ms)(Ns). Show that it takes an electron 36 min to drift through the two Nichrome wires from location B to location A. (c) On the other hand, about how long did it take to establish the steady state when the circuit was first assembled? Give a very approximate numerical answer, not a precise one. (d) There are about 9×1028mobile electrons per cubic meter in Nichrome. How many electrons cross the junction between the two wires every second?

You hang a 10 kg mass from a copper wire, and the wire stretches by .

(a)If you suspend the same mass from two copper wires, identical to the original wire, what happens?

(b)If you suspend the same mass from a copper wire with half the cross-sectional area but the same length as the original wire, what happens?

(c)If you suspend the same mass from a copper wire with the same cross-sectional area but twice the length of the original wire, what happens?

Question:A system is acted upon by two forces,18,47,-23Nand-20,-13,41N. What is the net force acting on the system?

(a) On a piece of graph paper, draw the vector f=<-2,4,0>, putting the tail of the vector at <-3,0,0>.Label the vector f.

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