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In the overhead view of Fig. (a), a 2.0 kg cookie tin is accelerated at 3.0 m/s^2 in the direction shown by a , over a frictionless horizontal surface. The acceleration is caused by three horizontal forces, only two of which are shown: F1 of magnitude 10 N and F2 of magnitude 20 N. What is the third force F3 in unit-vector notation and as a magnitude and an angle? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153857

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In a two-dimensional tug-of-war, Alex, Betty, and Charles pull horizontally on an automobile tire at the angles shown in the overhead view of Fig. (a). The tire remains stationary in spite of the three pulls. Alex pulls with force F-A of magnitude 220 N, and Charles pulls with force F_C of magnitude 170 N. The direction of is not given. What is the magnitude of Betty's force F_B .

Subject: Physics   |   Topic: Mechanics  |   ID: 153859

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Let us consider John Massis and the railroad cars, and assume that Massis pulled (with his teeth) on his end of the rope with a constant force that was 2.5 times his body weight, at an angle Teta of 30° from the horizontal. His mass m was 80 kg. The weight W of the cars was 700 kN, and he moved them 1.0 m along the rails. Assume that the rolling wheels encountered no retarding force from the rails. What was the speed of the cars at the end of the pull?

Subject: Physics   |   Topic: Mechanics  |   ID: 153860

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Figure shows a block S (the sliding block) with mass M = 3.3 kg. The block is free to move along a horizontal frictionless surface such as an air table. This first block is connected by a cord that wraps over a frictionless pulley to a second block H (the hanging block), with mass m = 2.1 kg. The cord and pulley have negligible masses compared to the blocks (they are "massless"). The hanging block H falls as the sliding block S accelerates to the right. Find a) the acceleration of the sliding block, (b) the acceleration of the hanging block, and (c) the tension in the cord.

Fig. a. A block S of mass M is connected to a block H of mass m by a cord that wraps over a pulley.

Fig.b. The forces acting on the two blocks of Fig. a.

Subject: Physics   |   Topic: Mechanics  |   ID: 153863

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In fig. (a), a block B of mass M = 15.0 kg hangs by a cord from a knot K of mass mk, which hangs from a ceiling by means of two other cords. The cords have negligible mass, and the magnitude of the gravitational force on the knot is negligible compared to the gravitational force on the block. What are the tensions in the cords?

Fig. (a) A block of mass M hangs from three cords by means of a knot. (b) A free-body diagram for the block, (c) A free-body diagram for the knot.

Subject: Physics   |   Topic: Mechanics  |   ID: 153866

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In Fig. (a), a cord holds stationary a block of mass m = 15 kg, on a frictionless plane that is inclined at angle Teta = 27°.
(a) What are the magnitudes of the force on the block from the cord and the normal force on the block from the plane?
(b) We now cut the cord. As the block then slides down the inclined plane, does it accelerate? If so, what is its acceleration?

Fig. (a) A block of mass m held stationary by a cord. (b) A free-body diagram for the block, (c) The x and y components of Fg.

Subject: Physics   |   Topic: Mechanics  |   ID: 153868

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In Fig.(a), a passenger of mass m = 72.2 kg stands on a platform scale in an elevator cab. We are concerned with the scale readings when the cab is stationary, and when it is moving up or down.

(a) Find a general solution for the scale reading, whatever the vertical motion of the cab.
(b) What does the scale read if the cab is stationary or moving upward at a constant 0.50 m/s?
(c) What does the scale read if the cab accelerates upward at 3.20 m/s2 and downward at 3.20 m/s2?
(d) During the upward acceleration in part (c), what is the magnitude Fnet of the net force on the passenger, and what is the magnitude ap,cab of the passenger's acceleration as measured in the frame of the cab?


Subject: Physics   |   Topic: Mechanics  |   ID: 153870

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In Fig. (a), a constant horizontal force F of magnitude 20 N is applied to block A of mass mA = 4.0 kg, which pushes against block B of mass mB = 6.0 kg. The blocks slide over a frictionless surface, along an x axis.
(a) What is the acceleration of the blocks?
(b) What is the force on block B from block A (Fig. (c))?


Subject: Physics   |   Topic: Mechanics  |   ID: 153872

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In Fig. (a), a student (with cleated boots) pushes a loaded sled of mass m = 240 kg through a displacement of magnitude d = 2.3 m along an x axis, over the frictionless surface of a frozen lake.

The student's force on the sled is horizontal and has a magnitude of 130 N, and the sled starts from rest. What is the sled's velocity at the end of the displacement?


Subject: Physics   |   Topic: Mechanics  |   ID: 153874

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In Fig. (a), a hand H pulls on a taut horizontal rope R (of mass m = 0.200 kg) that is attached to a block B (of mass M = 5.00 kg). The resulting acceleration of the rope and block across the frictionless surface has constant magnitude 0.300 m/s^2 and is directed in the positive direction of the x axis indicated in the figure. Note that this rope is not \\\"massless\\\" like those in Fig. and elsewhere in this chapter. We return to this feature in part (d).
(a) Identify all the third-law force pairs for the horizontal forces in Fig. (a) and show how the vectors in each pair are related.
(b) What is the magnitude of the force on the block from the rope?
(c) What is the magnitude of the force on the rope from the block?
(d) What is the magnitude of the force on the rope from the hand?


Subject: Physics   |   Topic: Mechanics  |   ID: 153876

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a) Find the acceleration a of the blocks on Fig. 1
b) Find tension T in the cord

Subject: Physics   |   Topic: Mechanics  |   ID: 153878

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Figure(a) shows two blocks connected by a cord that passes over a massless , frictionless pulley (the arrangement is known as Atwood's machine). The lighter block L has mass m = 1.3 kg and the heavier block H has mass M = 2.8 kg. Find the magnitudes of the accelerations of the two blocks and the magnitude T of the force on each block from the cord.


Subject: Physics   |   Topic: Mechanics  |   ID: 153882

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A bedroom bureau with a mass of 45 kg, including drawers and clothing, rests on the floor,
(a) If the coefficient of static friction between the bureau and the floor is 0.45, what is the magnitude of the minimum horizontal force that a person must apply to start the bureau moving?
(b) If the drawers and clothing, with 17 kg mass, are removed before the bureau is pushed, what is the new minimum magnitude? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153885

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The coefficient of static friction between Teflon and scrambled eggs is about 0.04. What is the smallest angle from the horizontal that will cause the eggs to slide across the bottom of a Teflon-coated skillet? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153886

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A baseball player with mass m = 79 kg, sliding into second base, is retarded by a frictional force of magnitude 470 N. What is the coefficient of kinetic friction Mu_k between the player and the ground? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153887

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The mysterious sliding stones. Along the remote Racetrack Playa in Death Valley, California, stones sometimes gouge out prominent trails in the desert floor, as if they had been migrating (Fig.6-4 ). For years curiosity mounted about why the stones moved. One explanation was that strong winds during the occasional rainstorms would drag the rough stones over ground softened by rain. When the desert dried out, the trails behind the stones were hard-baked in place. According to measurements, the coefficient of kinetic friction between the stones and the wet playa ground is about 0.80.
What horizontal force is needed on a stone of typical mass 20 kg to maintain the stone's motion once a gust has started it moving? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153889

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A person pushes horizontally with a force of 220 N on a 55kg crate to move it across a level floor. The coefficient of kinetic friction is 0.35.
(a) What is the magnitude of the frictional force?
(b) What is the magnitude of the crate's acceleration? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153890

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A house is built on the top of a hill with a nearby 45° slope (Fig. 6-6). An engineering study indicates that the slope angle should be reduced because the top layers of soil along the slope might slip past the lower layers. If the static coefficient of friction between two such layers is 0.5, what is the least angle Psi through which the present slope should be reduced to prevent slippage? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153892

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A 110 g hockey puck sent sliding over ice is stopped in 15m by the frictional force on it from the ice.
(a) If its initial speed 6.0 m/s, what is the magnitude of the frictional force?
(b) What is the coefficient of friction between the puck and the ice? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153893

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In Fig.6-8 , a 49 kg rock climber is climbing a \\\"chimney\\\". between two rock slabs. The static coefficient of friction between her shoes and the rock is 1.2; between her back and the rock it is 0.80. She has reduced her push against the rock until her back and her shoes are on the verge of slipping,
(a) Draw a free-body diagram of the climber,
(b) What is her push against the rock?
(c) What fraction of her weight is supported by the frictional force on her shoes? ...MORE

Subject: Physics   |   Topic: Mechanics  |   ID: 153895

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