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Chapter 2: Q2-3 (page 81)

You observe three carts moving to the left. Cart A moves to the left at nearly constant speed. Cart B moves to the left, gradually speeding up. Cart C moves to the left, gradually slowing down. Which cart or carts, if any, experience a net force to the left?

Short Answer

Expert verified

Cart B experiences a net force to the left.

Step by step solution

01

Definition of Net force

The net force, also known as the resultant force, is the sum of all forces acting on an item at the same time.

02

Find that when there is a net force to the left, whichever cart or carts are it?

  • Cart 'A' accelerates to the left at a near-constant rate.

  • Cart 'B' accelerates as it advances to the left.

  • Cart ‘C' moves to the left, swooping down gradually.

  • The net force acting on an object moving at constant speed is zero, hence there is no net force acting on cart 'A' toward the left.

  • When the item's velocity and force are in the same direction, the object will accelerate.

  • Because the Cart B is speeding up and travelling to the left, there is a net force operating on the cart 'B' to the left.

  • When the velocity and force directions are opposite, the item slows down.

  • Because the cart C is slowing down and travelling to the left, there is a net force operating on the cart 'C' to the right.

Thus, the Cart ‘B’ is the cart that is being pushed to the left by the net force.

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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?

A ball moves in the direction of the arrow labelled cin Figure 2.53The ball is struck by a stick that briefly exerts a force on the ball in the direction of the arrow labelled e. Which arrow best describes the direction of ∆p, the change in the ball's momentum?

If the magnitude of the electric field in air exceeds roughly 3×106N3, the air break down and a spark forms. For a two-disk capacitor of radius 51 cm with a gap of 2 mm, if the electric field inside is just high enough that a spark occurs, what is the strength of the fringe field just outside the center of the capacitor?

Question: the Hall effect can be used to determine the sign of the mobile charges in a particular conducting material. A bar of a new kind of conducting material is connected to a battery as shown in Figure 20.85. In this diagram, the x-axis runs to the right, the y-axis runs up, and the z-axis runs out of the page, toward you. A voltmeter is connected across the bar as shown, with the leads placed directly opposite each other along a vertical line. In order to answer the following question, you should draw a careful diagram of the situation, including all relevant charges, electric fields, magnetic fields, and velocities.

Initially, there is no magnitude filed in the region of the bar. (a) Inside the bar, what is the direction of the electric field E→due to the charges on the batteries and the surface of the wires and the bar? This is the electric field that drives the current in the bar. (b) If the mobile charges in the bar are positive in what direction do they move when the current runs? (c) If the mobile charges in the bar are negative, in what direction do they move when the current runs? (d) In this situation (zero magnetic fields), what is the sign of the reading on the voltmeter?

Next, large coils (not shown) are moved near the bar. And current runs through the coils, making a magnetic field in the -z direction (into the page). (e) If the mobile charges in the bar are negative, what is the direction of the magnetic force on the mobile charge? (f) If the mobile charges in the bar are negative, which of the following things will happen? (1) Positive charge will accumulate on the top of the bar. (2) The bar will not becomes polarized. (3) Negative charge will accumulate on the left end of the bar. (4) Negative charge will accumulate on the top of the bar. (g) If the mobile charges in the bar are positive, what is the direction of the magnetic force on the mobile charges? (h) If the mobile charges in the bar are positive, which of these things will happen? (1) positive charge will accumulate on the top of the bar. (2) The bar will not becomes polarized. (3) Positive charge will accumulate on the right end of the bar. (4) Negative charge will accumulate on the top of the bar.

You look at the voltmeter and find that the reading on the meter is -5×10-4volts. (i) What can you conclude from this observation? (Remember that a voltmeter gives a positive reading if the positive lead is attached to the higher potential location.) (1) There is not enough information to figure out the sign of the mobile charges. (2) The mobile charges are negative. (3) The mobile charges are positive.
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