Exam 8: Conservation of Energy

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 sliding on a horizontal frictionless surface is attached to one end of a horizontal spring (k = 200 N/m)which has its other end fixed.If the block has a speed of 4.0 m/s as it passes through the equilibrium position,what is its speed when it is 20 cm from the equilibrium position?

A spring (k = 600 N/m)is placed in a vertical position with its lower end supported by a horizontal surface.A 2.0-kg block that is initially 0.40 m above the upper end of the spring is dropped from rest onto the spring.What is the kinetic energy of the block at the instant it has fallen 0.50 m (compressing the spring 0.10 m)?

A pendulum is made by letting a 2.0-kg object swing at the end of a string that has a length of 1.5 m.The maximum angle the string makes with the vertical as the pendulum swings is 30°.What is the speed of the object at the lowest point in its trajectory?

A 1.5-kg block sliding on a rough horizontal surface is attached to one end of a horizontal spring (k = 200 N/m)which has its other end fixed.If this system is displaced 20 cm horizontally from the equilibrium position and released from rest,the block first reaches the equilibrium position with a speed of 2.0 m/s.What is the coefficient of kinetic friction between the block and the horizontal surface on which it slides?

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?

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

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 block is projected down a plane that makes an angle of 20° with the horizontal with an initial kinetic energy of 2.0 J.If the coefficient of kinetic friction between the block and plane is 0.40,how far will the block slide down the plane before coming to rest?

Cubical blocks of mass m and side l are piled up in a vertical column.The total gravitational potential energy of a column of three blocks is

A small lead sphere of mass m is hung from a spring of spring constant k.The gravitational potential energy of the system equals zero at the equilibrium position of the spring before the weight is attached.The total mechanical energy of the system when the mass is hanging at rest is

The two masses in the figure are released from rest.After the 3.0-kg mass has fallen 1.5 m,it is moving with a speed of 3.8 m/s.What is the change in mechanical energy done on the system during this time interval by the frictional force on the 2.0 kg mass?

A 1.2-kg mass is projected from ground level with a velocity of 30 m/s at some unknown angle above the horizontal.A short time after being projected,the mass barely clears a 16-m tall fence.Disregard air resistance and assume the ground is level.What is the kinetic energy of the mass as it clears the fence?

A 3.50 kg block is pulled along a moving conveyor belt at a constant speed of 0.500 m/s relative to a stationary observer while the belt moves at a constant speed of 0.200 m/s in the same direction.If the coefficient of kinetic friction is 0.400,the magnitude of the mechanical energy dissipated,in J,caused by the force of friction on the block in 8.00 s is

As a 1.0-kg object moves from point A to point B,it is acted upon by a single conservative force which does −40 J of work during this motion.At point A the speed of the particle is 6.0 m/s and the potential energy associated with the force is +50 J.What is the potential energy at point B?

As an object moves from point A to point B only two forces act on it: one force is conservative and does −70 J of work,the other force is nonconservative and does +50 J of work.Between A and B,

Which of the following is a conservative force? (All refer to a car on a slope. )

A spring with spring constant 800 N/m compressed 0.200 m is released and projects a 0.800 kg mass along a frictionless surface.The mass reaches a surface area where μ_k = 0.400 and comes to a stop.The following student solution contains at least one error.What is the error?

A champion athlete can produce one horsepower (746 W)for a short period of time.The number of 16 cm high steps a 70 kg athlete could ascend in one minute while expending one horsepower is

A 2.0-kg block sliding on a rough horizontal surface is attached to one end of a horizontal spring (k = 250 N/m)which has its other end fixed.The block passes through the equilibrium position with a speed of 2.6 m/s and first comes to rest at a displacement of 0.20 m from equilibrium.What is the coefficient of kinetic friction between the block and the horizontal surface?