6. Intro to Forces (Dynamics)

Newton's First & Second Laws

6. Intro to Forces (Dynamics)

Newton's First & Second Laws

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06:54

Intro to Forces & Newton's Second Law

Solving for Forces Using Newton's Second Law

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04:06

Newton's Second Law of Motion: F = ma

Professor Dave Explains

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Newton's First Law of Motion: Mass and Inertia

06:22

Newton's First Law of Motion: Mass and Inertia

Professor Dave Explains

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Anderson Video - Newton's Second Law

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Newton's First & Second Law Part 3 physics lesson

Newton's First & Second Law Part 2 physics lesson

Newton's First & Second Law Part 1 physics lesson

Newton's Three Laws of Motion (Clear and Easy to Follow)

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Multiple Choice

100 kg

rock is in space, far from any planets, stars or black holes. It is moving in a straight line at a constant

10,000 m / s

relative to our sun. What total force is required to keep it moving that fast?

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Multiple Choice

An elevator is going up at a constant speed in a very tall building. Assume the only forces acting on the elevator are a downward weight force and the force of a cable pulling the elevator up. Ignore air resistance and friction. How does the magnitude of the weight force compare to the magnitude of the force of the cable?

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Multiple Choice

10 N

horizontal force is applied to a

10 kg

box causing it to speed up. The force of kinetic friction is

5 N

. Which choice best describes the subsequent motion of the box?

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Textbook Question

A hockey puck with mass 0.160 kg is at rest at the origin (x = 0) on the horizontal, frictionless surface of the rink. At time t = 0 a player applies a force of 0.250 N to the puck, parallel to the x-axis; she continues to apply this force until t = 2.00s. (a) What are the position and speed of the puck at t = 2.00 s?

A small 8.00-kg rocket burns fuel that exerts a time-varying upward force on the rocket (assume constant mass) as the rocket moves upward from the launch pad. This force obeys the equation F = A + Bt2. Measurements show that at t = 0, the force is 100.0 N, and at the end of the first 2.00 s, it is 150.0 N. (a) Find the constants A and B, including their SI units

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Textbook Question

A 4.50-kg experimental cart undergoes an acceleration in a straight line (the x-axis). The graph in Fig. E4.13 shows this acceleration as a function of time. (b) During what times is the net force on the cart a constant?

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Textbook Question

A 4.50-kg experimental cart undergoes an acceleration in a straight line (the x-axis). The graph in Fig. E4.13 shows this acceleration as a function of time. (a) Find the maximum net force on this cart. When does this maximum force occur?

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Textbook Question

A hockey puck with mass 0.160 kg is at rest at the origin (x = 0) on the horizontal, frictionless surface of the rink. At time t = 0 a player applies a force of 0.250 N to the puck, parallel to the x-axis; she continues to apply this force until t = 2.00s. (b) If the same force is again applied at t = 5.00 s, what are the position and speed of the puck at t = 7.00 s?

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Textbook Question

A dockworker applies a constant horizontal force of 80.0 N to a block of ice on a smooth horizontal floor. The frictional force is negligible. The block starts from rest and moves 11.0 m in 5.00 s. (a) What is the mass of the block of ice?

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Textbook Question

A box rests on a frozen pond, which serves as a frictionless horizontal surface. If a fisherman applies a horizontal force with magnitude 48.0 N to the box and produces an acceleration of magnitude 2.20 m/s2, what is the mass of the box?

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Textbook Question

Due to a jaw injury, a patient must wear a strap (Fig. E4.3) that produces a net upward force of 5.00 N on his chin. The tension is the same throughout the strap. To what tension must the strap be adjusted to provide the necessary upward force?

To extricate an SUV stuck in the mud, workmen use three horizontal ropes, producing the force vectors shown in Fig. E4.2. (b) Use the components to find the magnitude and direction of the resultant of the three pulls.

To extricate an SUV stuck in the mud, workmen use three horizontal ropes, producing the force vectors shown in Fig. E4.2. (a) Find the x- and y-components of each of the three pulls.

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Textbook Question

Two dogs pull horizontally on ropes attached to a post; the angle between the ropes is 60.0°. If Rover exerts a force of 270 N and Fido exerts a force of 300 N, find the magnitude of the resultant force and the angle it makes with Rover's rope.

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Textbook Question

A man is dragging a trunk up the loading ramp of a mover's truck. The ramp has a slope angle of 20.0°, and the man pulls upward with a force F→ whose direction makes an angle of 30.0° with the ramp (Fig. E4.4). (b) How large will the component Fy perpendicular to the ramp be then?

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Textbook Question

A man is dragging a trunk up the loading ramp of a mover's truck. The ramp has a slope angle of 20.0°, and the man pulls upward with a force F→ whose direction makes an angle of 30.0° with the ramp (Fig. E4.4). (a) How large a force F→ is necessary for the component Fx parallel to the ramp to be 90.0 N?

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Textbook Question

II) Using focused laser light, optical tweezers can apply a force of about 10 pN (piconewtons) to a 1.0-μm-diameter polystyrene bead, which has a density about equal to that of water: a volume of 1.0 cm³ has a mass of about 1.0 g. Estimate the bead's acceleration in g's.

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Textbook Question

(II) A high-speed 14-car Italian train has a mass of 640 metric tons (640,000 kg). It can exert a maximum force of 400 kN horizontally against the tracks, whereas at maximum constant velocity (300 km/h), it exerts a force of about 150 kN. Calculate

a) its maximum acceleration, and (b) estimate the total force of friction and air resistance at top speed.

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Textbook Question

(II) Superman must stop a 120-km/h train in 150 m to keep it from hitting a stalled car on the tracks. If the train's mass is 3.6 x 10⁵ kg , how much force must he exert? Compare to the weight of the train (give as %). How much force does the train exert on Superman?

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Textbook Question

An 18-kg child is riding in a child-restraint chair, securely fastened to the seat of a car (Fig. 4–69). Assume the car has speed 45 km/h when it hits a tree and is brought to rest in 0.20 s. Assuming constant deceleration during the collision, estimate the net horizontal force F that the straps of the restraint chair exert on the child to hold her in the chair. <IMAGE>

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Textbook Question

When jumping straight up from a crouched position, an average person can reach a maximum height of about 60 cm. During the jump, the person's body from the knees up typically rises a distance of around 50 cm. To keep the calculations simple and yet get a reasonable result, assume that the entire body rises this much during the jump. (b) Draw a free-body diagram of the person during the jump.

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Textbook Question

What is the acceleration, as a multiple of g, if this force is applied to a 110 kg bicyclist? This is the combined mass of the cyclist and the bike.

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Textbook Question

If a car stops suddenly, you feel 'thrown forward.' We'd like to understand what happens to the passengers as a car stops. Imagine yourself sitting on a very slippery bench inside a car. This bench has no friction, no seat back, and there's nothing for you to hold onto. d. Describe what happens to you as the car slows down.

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Textbook Question

On September 8, 2004, the Genesis spacecraft crashed in the Utah desert because its parachute did not open. The 210-kg capsule hit the ground at 311 km/h and penetrated the soil to a depth of 81.0 cm. (a) What was its acceleration (in m/s2 and in g's), assumed to be constant, during the crash?

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Textbook Question

An astronaut is inside a 2.25 × 106 kg rocket that is blasting off vertically from the launch pad. You want this rocket to reach the speed of sound (331 m/s) as quickly as possible, but astronauts are in danger of blacking out at an acceleration greater than 4g. (b) What force, in terms of the astronaut's weight w, does the rocket exert on her? Start with a free-body diagram of the astronaut.

An astronaut is inside a 2.25 × 106 kg rocket that is blasting off vertically from the launch pad. You want this rocket to reach the speed of sound (331 m/s) as quickly as possible, but astronauts are in danger of blacking out at an acceleration greater than 4g. (a) What is the maximum initial thrust this rocket's engines can have but just barely avoid blackout? Start with a free-body diagram of the rocket.

A light rope is attached to a block with mass 4.00 kg that rests on a frictionless, horizontal surface. The horizontal rope passes over a frictionless, massless pulley, and a block with mass m is suspended from the other end. When the blocks are released, the tension in the rope is 15.0 N. (a) Draw two free-body diagrams: one for each block.

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Textbook Question

On September 8, 2004, the Genesis spacecraft crashed in the Utah desert because its parachute did not open. The 210-kg capsule hit the ground at 311 km/h and penetrated the soil to a depth of 81.0 cm. (b) What force did the ground exert on the capsule during the crash? Express the force in newtons and as a multiple of the capsule's weight.

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Textbook Question

Problems 35, 36, 37, 38, 39, and 40 show a free-body diagram. For each: a. Identify the direction of the acceleration vector a and show it as a vector next to your diagram. Or, if appropriate, write a = 0.

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Textbook Question

FIGURE EX5.14 shows an object's acceleration-versus-force graph. What is the object's mass?

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Textbook Question

A constant force is applied to an object, causing the object to accelerate at 10 m/s². What will the acceleration be if d. The force is halved and the object's mass is doubled?

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Textbook Question

A constant force is applied to an object, causing the object to accelerate at 10 m/s². What will the acceleration be if a. The force is halved?

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Textbook Question

A single force with x-component Fₓ acts on a 2.0 kg object as it moves along the x-axis. A graph of Fₓ versus t is shown in FIGURE P5.32. Draw an acceleration graph aₓ versus t) for this object.

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Textbook Question

A single force with x-component Fₓ acts on a 500 g object as it moves along the x-axis. The object's acceleration graph aₓ versus t) is shown in FIGURE P5.30. Draw a graph of Fₓ versus t.

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Textbook Question

The 100 kg block in FIGURE EX7.24 takes 6.0 s to reach the floor after being released from rest. What is the mass of the block on the left? The pulley is massless and frictionless.

Two blocks are attached to opposite ends of a massless rope that goes over a massless, frictionless, stationary pulley. One of the blocks, with a mass of 6.0 kg, accelerates downward at 3/4g. What is the mass of the other block?

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Textbook Question

(II) A 27-kg chandelier hangs from a ceiling on a vertical 3.4-m-long wire.

(a) What horizontal force would be necessary to displace its position 0.15 m to one side?

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Textbook Question

(II) A 27-kg chandelier hangs from a ceiling on a vertical 3.4-m-long wire.

(b) What will be the tension in the wire?

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Textbook Question

II) According to a simplified model of a mammalian heart, at each pulse approximately 20 g of blood is accelerated from 0.25 m/s to 0.35 m/s during a period of 0.10 s. What is the magnitude of the force exerted by the heart muscle?

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Textbook Question

(III) A person jumps from the roof of a house 2.8 m high. When he strikes the ground below, he bends his knees so that his torso decelerates over an approximate distance of 0.70 m. If the mass of his torso (excluding legs) is 42 kg, find

(b) the average force exerted on his torso by his legs during deceleration.

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Textbook Question

(II) An object is hanging by a string from your rearview mirror. While you are accelerating at a constant rate from rest to 28 m/s in 5.0 s, what angle θ does the string make with the vertical? See Fig. 4–46.

<IMAGE>

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Textbook Question

A package of mass m is placed onto a horizontal conveyor belt moving at speed v (Fig. 7–32). The coefficient of kinetic friction between package and belt is μₖ .

<IMAGE>

(a) How long does it take the package to stop sliding on the belt? [Hint: Use F = ma.]

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Textbook Question

(II) A 3.0-kg object has the following two forces acting on it:

→

F₁ = (16î + 12ĵ) N

→

F ₂ = ( -10î + 22ĵ) N

If the object is initially at rest, determine its velocity v→ at t = 4.0s .

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