Exam 7: Conservation of Energy

A 3.0-kg block is on a horizontal surface.The block is at rest when,at t = 0,a force (magnitude P = 12 N)acting parallel to the surface is applied to the block causing it to accelerate.The coefficient of kinetic friction between the block and the surface is 0.20.At what rate is the force P doing work on the block at t = 2.0 s?

(Multiple Choice)

4.9/5

(73)

Question 41

Two masses,M_A and M_B,with M_B = 2M_A,are released at the same time and allowed to fall straight down.Neglect air resistance.When we compare their kinetic energies after they have fallen equal distances,we find that

(Multiple Choice)

5.0/5

(79)

Question 42

While running,a person dissipates about 0.6 J of mechanical energy per step per kilogram of body mass.If a 60-kg person runs with a power of 70 Watts during a race,how fast is the person running? Assume a running step is 1.5 m long.

(Short Answer)

4.8/5

(76)

Question 43

A skier weighing 0.70 kN goes over a frictionless circular hill as shown.If the skier's speed at point A is 9.2 m/s,what is his speed at the top of the hill (point B)?

(Multiple Choice)

4.8/5

(88)

Question 44

A 2.0-kg mass is projected vertically upward from ground level with an initial speed of 30 m/s.The mass rises to a maximum height of 35 m above ground level.What is the change in mechanical energy of the mass caused by air resistance between the point of projection and the point of maximum height?

(Multiple Choice)

4.7/5

(62)

Question 45

A 2.0-kg mass is projected from the edge of the top of a 20-m tall building with a velocity of 24 m/s at some unknown angle above the horizontal.Disregard air resistance and assume the ground is level.What is the kinetic energy of the mass just before it strikes the ground?

(Multiple Choice)

5.0/5

(80)

Question 46

A 2.0-kg block slides down a fixed,rough curved track.The block has a speed of 5.0 m/s after its height above a horizontal surface has decreased by 1.8 m.Assume the block starts from rest.What is the change in mechanical energy of the block caused by the force of friction during this descent?

(Multiple Choice)

4.9/5

(78)

Question 47

A 0.04-kg ball is thrown from the top of a 30-m tall building (point A)at an unknown angle above the horizontal.As shown in the figure,the ball attains a maximum height of 10 m above the top of the building before striking the ground at point B.If air resistance is negligible,what is the value of the kinetic energy of the ball at B minus the kinetic energy of the ball at A (K_B - K_A)?

(Multiple Choice)

4.7/5

(59)

Question 48

A particle is acted upon by only two forces,one conservative and one nonconservative and neither being a force of friction,as it moves from point A to point B.The kinetic energies of the particle at points A and B are equal if

(Multiple Choice)

4.8/5

(90)

Question 49

Objects A and B,of mass M and 2M respectively,are each pushed a distance d straight up an inclined plane by a force F parallel to the plane.The coefficient of kinetic friction between each mass and the plane has the same value $\mu$ _k.At the highest point,

(Multiple Choice)

4.8/5

(70)

Question 50

A simple pendulum,2.0 m in length,is released from rest when the support string is at an angle of 25 $\degree$ from the vertical.What is the speed of the suspended mass at the bottom of the swing?

(Short Answer)

4.8/5

(85)

Question 51

A 6.0-kg block slides along a horizontal surface.If µ_k = 0.20 for the block and surface,at what rate is the friction force changing the mechanical energy of the block at an instant when its speed is 4.0 m/s?

(Multiple Choice)

4.9/5

(91)

Question 52

A surprising demonstration involves dropping an egg from a third-floor window to land on a foam-rubber pad 2 in (5 cm)thick without breaking.If a 56-gram egg falls 12 m,and the foam pad stops the egg in 6.25 ms,by how much is the pad compressed?

(Short Answer)

4.8/5

(76)

Question 53

Starting from rest at t = 0,a 5.0-kg block is pulled across a horizontal surface by a constant horizontal force having a magnitude of 12 N.If the coefficient of friction between the block and the surface is 0.20,at what rate is the 12-N force doing work at t = 5.0 s?

(Multiple Choice)

4.7/5

(77)

Question 54

A 20-kg mass is fastened to a light spring (k = 380 N/m)that passes over a pulley as shown.The pulley is frictionless,and the mass is released from rest when the spring is unstretched.After the mass has dropped 0.40 m,what is its speed?

(Multiple Choice)

4.9/5

(74)

Question 55

A 2.5-kg object suspended from the ceiling by a string that has a length of 2.5 m is released from rest with the string 40 $\degree$ below the horizontal position.What is the tension in the string at the instant when the object passes through its lowest position?

(Multiple Choice)

4.8/5

(69)

Question 56

A 12-kg projectile is launched with an initial vertical speed of 20 m/s.It rises to a maximum height of 18 m above the launch point.What is the change in mechanical energy caused by the dissipative (air)resistive force on the projectile during this ascent?

(Multiple Choice)

4.9/5

(85)

Question 57

An archer pulls her bow string back 0.40 m by exerting a force that increases uniformly from zero to 240 N.What is the equivalent spring constant of the bow,and how much work is done in pulling the bow?

(Short Answer)

4.7/5

(85)

Question 58

A rain cloud contains 2.66 * 10⁷ kg of water vapor.How long would it take for a 2.0 kW pump to lift the same amount of water to an altitude of 2 000 m?

(Short Answer)

4.7/5

(63)

Question 59

A 70-kg high jumper leaves the ground with a vertical velocity of 6.0 m/s.How high can he jump?

(Short Answer)

4.9/5

(95)

Question 60

Showing 41 - 60 of 77

Exam 7: Conservation of Energy

Two masses,MA and MB,with MB = 2MA,are released at the same time and allowed to fall straight down.Neglect air resistance.When we compare their kinetic energies after they have fallen equal distances,we find that

While running,a person dissipates about 0.6 J of mechanical energy per step per kilogram of body mass.If a 60-kg person runs with a power of 70 Watts during a race,how fast is the person running? Assume a running step is 1.5 m long.

A skier weighing 0.70 kN goes over a frictionless circular hill as shown.If the skier's speed at point A is 9.2 m/s,what is his speed at the top of the hill (point B)?

A 2.0-kg mass is projected vertically upward from ground level with an initial speed of 30 m/s.The mass rises to a maximum height of 35 m above ground level.What is the change in mechanical energy of the mass caused by air resistance between the point of projection and the point of maximum height?

A 2.0-kg mass is projected from the edge of the top of a 20-m tall building with a velocity of 24 m/s at some unknown angle above the horizontal.Disregard air resistance and assume the ground is level.What is the kinetic energy of the mass just before it strikes the ground?

A 2.0-kg block slides down a fixed,rough curved track.The block has a speed of 5.0 m/s after its height above a horizontal surface has decreased by 1.8 m.Assume the block starts from rest.What is the change in mechanical energy of the block caused by the force of friction during this descent?

A particle is acted upon by only two forces,one conservative and one nonconservative and neither being a force of friction,as it moves from point A to point B.The kinetic energies of the particle at points A and B are equal if

Objects A and B,of mass M and 2M respectively,are each pushed a distance d straight up an inclined plane by a force F parallel to the plane.The coefficient of kinetic friction between each mass and the plane has the same value μ\muμ k.At the highest point,

A simple pendulum,2.0 m in length,is released from rest when the support string is at an angle of 25 °\degree° from the vertical.What is the speed of the suspended mass at the bottom of the swing?

A 6.0-kg block slides along a horizontal surface.If µk = 0.20 for the block and surface,at what rate is the friction force changing the mechanical energy of the block at an instant when its speed is 4.0 m/s?

A surprising demonstration involves dropping an egg from a third-floor window to land on a foam-rubber pad 2 in (5 cm)thick without breaking.If a 56-gram egg falls 12 m,and the foam pad stops the egg in 6.25 ms,by how much is the pad compressed?

Starting from rest at t = 0,a 5.0-kg block is pulled across a horizontal surface by a constant horizontal force having a magnitude of 12 N.If the coefficient of friction between the block and the surface is 0.20,at what rate is the 12-N force doing work at t = 5.0 s?

A 20-kg mass is fastened to a light spring (k = 380 N/m)that passes over a pulley as shown.The pulley is frictionless,and the mass is released from rest when the spring is unstretched.After the mass has dropped 0.40 m,what is its speed?

A 2.5-kg object suspended from the ceiling by a string that has a length of 2.5 m is released from rest with the string 40 °\degree° below the horizontal position.What is the tension in the string at the instant when the object passes through its lowest position?

A 12-kg projectile is launched with an initial vertical speed of 20 m/s.It rises to a maximum height of 18 m above the launch point.What is the change in mechanical energy caused by the dissipative (air)resistive force on the projectile during this ascent?

An archer pulls her bow string back 0.40 m by exerting a force that increases uniformly from zero to 240 N.What is the equivalent spring constant of the bow,and how much work is done in pulling the bow?

A rain cloud contains 2.66 * 107 kg of water vapor.How long would it take for a 2.0 kW pump to lift the same amount of water to an altitude of 2 000 m?

A 70-kg high jumper leaves the ground with a vertical velocity of 6.0 m/s.How high can he jump?

Introduction and Vectors

Motion in One Dimension

Motion in Two Dimensions

The Laws of Motion

More Applications of Newtons Laws

Energy of a System

Momentum and Collisions

Relativity

Rotational Motion

Gravity,planetary Orbits,and the Hydrogen Atom

Oscillatory Motion

Mechanical Waves

Superposition and Standing Waves

Fluid Mechanics

Temperature and the Kinetic Theory of Gases

Energy in Thermal Processes: the First Law of Thermodynamics

Heat Engines,entropy,and the Second Law of Thermodynamics

Electric Forces and Electric Fields

Electric Potential and Capacitance

Current and Direct Current Circuits

Magnetic Forces and Magnetic Fields

Faradays Law and Inductance

Electromagnetic Waves

Reflection and Refraction of Light

Image Formation by Mirrors and Lenses

Wave Optics

Quantum Physics

Atomic Physics

Nuclear Physics

Particle Physics

Filters

Two masses,M_A and M_B,with M_B = 2M_A,are released at the same time and allowed to fall straight down.Neglect air resistance.When we compare their kinetic energies after they have fallen equal distances,we find that

Objects A and B,of mass M and 2M respectively,are each pushed a distance d straight up an inclined plane by a force F parallel to the plane.The coefficient of kinetic friction between each mass and the plane has the same value $\mu$ _k.At the highest point,

A simple pendulum,2.0 m in length,is released from rest when the support string is at an angle of 25 $\degree$ from the vertical.What is the speed of the suspended mass at the bottom of the swing?

A 6.0-kg block slides along a horizontal surface.If µ_k = 0.20 for the block and surface,at what rate is the friction force changing the mechanical energy of the block at an instant when its speed is 4.0 m/s?

A 2.5-kg object suspended from the ceiling by a string that has a length of 2.5 m is released from rest with the string 40 $\degree$ below the horizontal position.What is the tension in the string at the instant when the object passes through its lowest position?

A rain cloud contains 2.66 * 10⁷ kg of water vapor.How long would it take for a 2.0 kW pump to lift the same amount of water to an altitude of 2 000 m?