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A 75.0-kg woman stands on a bathroom scale in an elevator that accelerates from rest to 30.0 m/s in 2.00 s. (a) Calculate the scale reading in newtons and compare it with her weight. (The scale exerts an upward force on her equal to its reading.) (b) What is unreasonable about the result? (c) Which premise is unreasonable, or which premises are inconsistent?

a. 1860 N, 2.53; b. The value (1860 N) is more force than you expect to experience on an elevator. The force of 1860 N is 418 pounds, compared to the force on a typical elevator of 904 N (which is about 203 pounds); this is calculated for a speed from 0 to 10 miles per hour, which is about 4.5 m/s, in 2.00 s). c. The acceleration a = 1.53 × g is much higher than any standard elevator. The final speed is too large (30.0 m/s is VERY fast)! The time of 2.00 s is not unreasonable for an elevator.

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(a) Calculate the minimum coefficient of friction needed for a car to negotiate an unbanked 50.0 m radius curve at 30.0 m/s. (b) What is unreasonable about the result? (c) Which premises are unreasonable or inconsistent?

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As shown below, if M = 5.50 kg, what is the tension in string 1?

Mass M is suspended from strings 1 and 2. String 1 connects to a wall at a point below and to the left of the mass. String 1 makes an angle of 40 degrees below the horizontal. String 2 connects to a ceiling at a point above and to the right of the mass. String 2 makes an angle of 40 degrees to the right of vertical.

189 N

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As shown below, if F = 60.0 N and M = 4.00 kg, what is the magnitude of the acceleration of the suspended object? All surfaces are frictionless.

Two blocks are shown. One block, labeled 2 M is on a horizontal table. A force F pulls on the 2 M block up and to the left at an angle of 30 degrees above the horizontal. On the opposite side, the block is connected to a string that pulls it to the right. The string passes over a pulley at edge of the table, then hangs straight down and connects to  the second block, labeled M. Block 2 is not in contact with the ramp.
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As shown below, if M = 6.0 kg, what is the tension in the connecting string? The pulley and all surfaces are frictionless.

Two blocks, both mass M are connected by a string that passes over a pulley between the blocks. The upper block is on a surface that slopes down and to the right at an angle of 30 degrees to the horizontal. The pulley is attached to the corner at the bottom of the slope, where the surface then bends and goes vertically down. The lower mass hangs straight down. It is not in contact with the surface.

15 N

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A small space probe is released from a spaceship. The space probe has mass 20.0 kg and contains 90.0 kg of fuel. It starts from rest in deep space, from the origin of a coordinate system based on the spaceship, and burns fuel at the rate of 3.00 kg/s. The engine provides a constant thrust of 120.0 N. (a) Write an expression for the mass of the space probe as a function of time, between 0 and 30 seconds, assuming that the engine ignites fuel beginning at t = 0 . (b) What is the velocity after 15.0 s? (c) What is the position of the space probe after 15.0 s, with initial position at the origin? (d) Write an expression for the position as a function of time, for t > 30.0 s .

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A half-full recycling bin has mass 3.0 kg and is pushed up a 40.0 ° incline with constant speed under the action of a 26-N force acting up and parallel to the incline. The incline has friction. What magnitude force must act up and parallel to the incline for the bin to move down the incline at constant velocity?

12 N

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A child has mass 6.0 kg and slides down a 35 ° incline with constant speed under the action of a 34-N force acting up and parallel to the incline. What is the coefficient of kinetic friction between the child and the surface of the incline?

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Additional problems

The two barges shown here are coupled by a cable of negligible mass. The mass of the front barge is 2.00 × 10 3 kg and the mass of the rear barge is 3.00 × 10 3 kg . A tugboat pulls the front barge with a horizontal force of magnitude 20.0 × 10 3 N, and the frictional forces of the water on the front and rear barges are 8.00 × 10 3 N and 10.0 × 10 3 N, respectively. Find the horizontal acceleration of the barges and the tension in the connecting cable.

An illustration showing a tug boat pulling two barges. The barge directly attached to the tug boat has mass 2.00 times 10 to the third kilograms. The barge at the end,  behind the first barge, has mass 3.00 times 10 to the third kilograms.

a x = 0.40 m/s 2 and T = 11.2 × 10 3 N

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Questions & Answers

velocity is a physician vector quantity; both magnitude and direction needed to define it. the scalar absolute value ( magnitude) of velocity is called "speed being a coherent derived unite whose quantity is measured in SI ( metric system) as metres per second (m/s) or SI base unit of (m . s^-1).
Kessy Reply
number of lines passing through area which is placed at some angle. these line are are produced by charge(+ or -).
M. Reply
hstjsbks
Junaid Reply
define electric flux? find the electric field due to a long strainght line
Aslam Reply
Clay Matthews, a linebacker for the Green Bay Packers, can reach a speed of 10.0 m/s. At the start of a play, Matthews runs downfield at 43° with respect to the 50-yard line (the +x-axis) and covers 7.8 m in 1 s. He then runs straight down the field at 90° with respect to the 50-yard line (that is, in the +y-direction) for 17 m, with an elapsed time of 2.9 s. (Express your answers in vector form.) (a) What is Matthews's final displacement (in m) from the start of the play?
Justin Reply
What is his average velocity (in m/s)?
Justin
A machine at a post office sends packages out a chute and down a ramp to be loaded into delivery vehicles. (a) Calculate the acceleration of a box heading down a 17.4° slope, assuming the coefficient of friction for a parcel on waxed wood is 0.100. (b) Find the angle of the slope down which this box could move at a constant velocity. You can neglect air resistance in both parts.
Austin Reply
what principle is applicable in projectile motion
Mkapa Reply
does rocket and satellite follow the same principle??? which principle do both of these follow???
Abhishek Reply
According to d'Broglie's concept of matter waves matter behaves like wave and the wavelength is h/p. but actually there is not only a wave but a wave packet wich is defined by a wave function and that wave function can defines everything about the particle but restricted by the uncertainty principle
Ravi Reply
what phenomenon describes Matter behave as a wave???
SHAKIRU Reply
simple definition of wave
Prajwal Reply
hello
Carls Reply
can anyone help me with this problem
Carls
A projectile is shot at a hill, the base of which is 300 m away. The projectile is shot at 60°60° above the horizontal with an initial speed of 75 m/s. The hill can be approximated by a plane sloped at 20°20° to the horizontal. Relative to the coordinate system shown in the following figure, the equation of this straight line is y=(tan20°)x−109.y=(tan20°)x−109. Where on the hill does the projectile land?
Carls
what is velocity
Abel Reply
hi, Musa,this moment a lateral
Arzoodan Reply
what is moment
Musa Reply
Practice Key Terms 2

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Source:  OpenStax, University physics volume 1. OpenStax CNX. Sep 19, 2016 Download for free at http://cnx.org/content/col12031/1.5
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