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Physics

Learn the toughest concepts covered in Physics with step-by-step video tutorials and practice problems by world-class tutors

6. Intro to Forces (Dynamics)

Newton's First & Second Laws

15 videos18 questions

VIDEOS 15

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PRACTICE 18

Multiple Choice
A $100 kg$ 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
A $10 N$ 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
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.
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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. (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.
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Textbook Question
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
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? (image)
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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? (image)
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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? (image)
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Textbook Question
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. (image)
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Textbook Question
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. (image)
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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
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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Types Of Forces & Free Body Diagrams

17 videos8 questions

VIDEOS 17

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PRACTICE 8

Forces & Kinematics

7 videos3 questions

VIDEOS 7

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PRACTICE 3

Vertical Forces & Acceleration

9 videos15 questions

VIDEOS 9

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PRACTICE 15

Vertical Equilibrium & The Normal Force

13 videos1 question

VIDEOS 13

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PRACTICE 1

Multiple Choice
A 3-kg box of junk is being lowered on a string at a constant speed. What is the tension in the string?
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Forces in 2D

8 videos6 questions

VIDEOS 8

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PRACTICE 6

Equilibrium in 2D

3 videos2 questions

VIDEOS 3

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PRACTICE 2

Newton's Third Law & Action-Reaction Pairs

9 videos8 questions

VIDEOS 9

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PRACTICE 8

Forces in Connected Systems of Objects

19 videos4 questions

VIDEOS 19

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PRACTICE 4

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