Exam 7: Work and Energy

Find the how much mechanical energy was converted to internal energy in the system box-surface-Earth when a box moves in a complete circle of radius $1.82 \mathrm {~m}$ on a uniform horizontal floor.The coefficient of kinetic friction between the floor and the box is 0.25,and the box weighs $65.0 \mathrm {~N}$

If 4.0 J of work are performed in stretching an ideal spring with a spring constant of 2500 N/m,by what distance is the spring stretched?

The kinetic friction force that a horizontal surface exerts on a 60.0-kg object is 50.0 N.If the initial speed of the object is 25.0 m/s,what distance will it slide before coming to a stop?

A stone is held at a height h above the ground.A second stone with four times the mass of the first one is held at the same height.The gravitational potential energy of the second stone-Earth system compared to that of the first stone-Earth system is

Joe and Bill throw identical balls vertically upward.Joe throws his ball with an initial speed twice as high as Bill.Assuming there is no air resistance,the maximum height of Joe's ball will be

A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs.Both springs were initially compressed by the same amount.Which of the following statements about these darts are correct? (There could be more than one correct choice.)

An ideal spring has a spring constant of 2500 N/m.is stretched 4.0 cm.How much work is required to stretch the spring by 4.0 cm?

How much work would a child do while pulling a 12-kg wagon a distance of $4.3 \mathrm {~m}$ exerting a $22 \mathrm {~N}$ force?

A small but dense 2.0-kg stone is attached to one end of a very light rod that is 1.2 m long.The other end of the rod is attached to a frictionless pivot.The rod is raised until it is vertical,with the stone above the pivot.The rod is released and the stone moves in a vertical circle with no air resistance.What is the force that the rod exerts on the stone as the stone moves through the bottom of the circle?

A 10-kg dog is running with a speed of 5.0 m/s.What is the minimum work required to stop the dog in 2.40 s?

What is the minimum energy needed to lift a 1.0-kg rocket to a height of 200 km and to give it a speed of 8.0 km/s at that height? (Neglect air resistance and the small decrease in g over that distance.)

If the work done to stretch an ideal spring by 4.0 cm is 6.0 J,what is the spring constant of this spring?

The momentum of an isolated system is conserved

Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg object moving at 20 m/s?

If you want to double the kinetic energy of a gas molecule,by what factor must you increase its momentum?

A 550-g ball traveling at 8.0 m/s undergoes a sudden head-on elastic collision with a 250-g ball traveling toward it also at 8.0 m/s.What is the speed of the 250-g mass just after the collision?

A 50-g ball moving at 10 m/s in the +x direction suddenly collides head-on with a stationary ball of mass 100 g.If the collision is perfectly elastic,what is the velocity of each ball immediately after the collision?

A 340-g air track cart traveling at 1.25 m/s suddenly collides elastically with a stationary 300-g cart.What is the speed of the 300-g cart just after the collision?

A tennis ball bounces on the floor three times,and during each bounce 23% of its kinetic energy (assuming that at the collision with the floor the ball-Earth system only had kinetic energy)is converted to internal energy..How high does it go after the third bounce,if we released it 4.0 m from the floor?

As shown in the figure,a 4.0-kg block is moving at 5.0 m/s along a horizontal frictionless surface toward an ideal spring that is attached to a wall.After the block collides with the spring,the spring is compressed a maximum distance of 0.68 m.What is the speed of the block when the spring is compressed to only one-half of the maximum distance?