Exam 7: Work and Energy

A small 1.4-N stone slides down a frictionless bowl,starting from rest at the rim.The bowl itself is a hemisphere of radius 75 cm.Just as the stone reaches the bottom of the bowl,how hard is the bowl pushing on it?

A person stands on the edge of a cliff.She throws three identical rocks with the same speed.Rock X is thrown vertically upward,rock Y is thrown horizontally,and rock Z is thrown vertically downward.If the ground at the base of the cliff is level,which rock hits the ground with the greatest speed if there is no air resistance?

You slam on the brakes of your car in a panic,and skid a certain distance on a straight level road.If you had been traveling twice as fast,what distance would the car have skidded,under the same conditions?

In a certain nuclear reactor,neutrons suddenly collide with deuterons,which have twice the mass of neutrons.In a head-on elastic collision with a stationary deuteron,what fraction of the initial kinetic energy of a neutron is transferred to the deuteron?

In 1994,fragments of Comet P/Shoemaker-Levy 9 collided with Jupiter.Assume that these fragments came from very very far away with no initial speed,and neglect the effect of the sun.What was their speed when they neared Jupiter's surface at a distance of 71.4 × 10⁶ m from its center? Jupiter has a mass of 1.90 × 10²⁷ kg,and G = 6.67 × 10^-11 N ∙ m²/kg².

A 0.32-kg ball is moving horizontally at 30 m/s just before suddenly bouncing off a wall Just after the bounce,it is moving horizontally at 25 m/s but in the opposite direction. (a)What is the magnitude of the change in momentum of the ball during the bounce? (b)What percentage of the ball's original kinetic energy was lost in the collision?

The sum of the forces exerted on a 1000-kg car while it is slowing down from 30 m/s to 15.9 m/s is 9500 N.How far does it travel while slowing down?

In the figure,determine the character of the collision.The masses of the blocks,and the velocities before and after,are shown.The collision is

Matthew pulls his little sister Sarah along the horizontal ground in a wagon.He exerts a force on the wagon of 60.0 N at an angle of 37.0° above the horizontal.If he pulls her a distance of 12.0 m,how much work does Matthew do?

A prankster drops a water balloon from the top of a building.If the balloon is traveling at 29.1 m/s when it strikes a window ledge that is 1.5 m above the ground,how tall is the building? Neglect air resistance.

What mass would have to be compressed to a radius of 1.0 × 10^-15 m (the order of magnitude of the radius of an atomic nucleus)in order for it to become a black hole? (G = 6.67 × 10^-11 N ∙ m²/kg²,c = 3.0 × 10⁸ m/s)

A typical incandescent light bulb consumes 75 W of power and has a mass of 30 g.You want to save electrical energy by dropping the bulb from a height great enough so that the kinetic energy of the bulb when it reaches the floor will be the same as the energy it took to keep the bulb on for 1.0 hour.From what height should you drop the bulb,assuming no air resistance and constant g?

A heavy rock and a light rock are dropped from the same height.The forces exerted on them by air are negligible.Which of the following statements about these rocks are correct? (There could be more than one correct choice.)

Planet A has twice the mass of Planet B.From this information,what can we conclude about the escape speed for Planet A compared to that of Planet B?

A family goes on vacation for one week but forgets to turn off an electric fan that consumes electricity at the rate of 200 W.If the cost of electricity is 12.0¢/kW∙h how much does it cost (to the nearest penny)to run the fan for the week?

A 10-N toy rocket blasts straight up from ground level with an initial kinetic energy of 40 J.At the exact top of its trajectory,the total mechanical energy of the rocket-Earth system is 140 J.To what vertical height above the ground does it rise,assuming no air resistance?

If electricity costs 7.06¢/kW∙h,how much would it cost you to run a $120 - W$ stereo system $\text { 4.0 hours }$ per day for $4.0 \text { weeks? }$

When you drop a pebble from height H,it reaches the ground with kinetic energy K assuming there is no air resistance.From what height should you drop it so it will reach the ground with twice as much kinetic energy?

A 10-kg object,hung by an ideal spring,causes the spring to stretch 2.0 cm.What is the spring constant for this spring?

A 4.0 kg object is moving with speed 2.0 m/s.A 1.0 kg object is moving with speed 4.0 m/s.The same stopping force is exerted on both objects and both objects are brought to rest.Which object travels the greater distance before stopping?