Exam 7: Work and Energy

In a police rifle test,a 15-g bullet traveling 213 m/s in a vertical direction suddenly buries itself in a 2.4-kg block of wood at rest directly above it.As a result,the bullet-block combination moves vertically upward. (a)Determine the velocity of the bullet-block combination just after the impact. (b)Determine the maximum height reached by the bullet/block combination. (c)Is kinetic energy conserved in this collision?

A 60-kg skier starts from rest from the top of a 50-m high slope.If the work done by friction is -6.0 kJ,what is the speed of the skier on reaching the bottom of the slope?

A 0.140-kg baseball is dropped from rest from a height of 2.20 m above the ground and experiences negligible air resistance as it falls.It rebounds to a height of 1.60 m.What change in the ball's momentum occurs as it rebounds from the ground?

Planet X-39 has a mass equal to 1/3 that of Earth and a radius equal to 1/3 that of Earth.If V is the escape speed for Earth,what is the escape speed for X-39?

How much work must be done by frictional forces in slowing a 1000-kg car from $26.1 \mathrm {~m} / \mathrm { s }$ to rest?

A sand mover at a quarry lifts 2,000 kg of sand per minute a vertical distance of 12 m.The sand is initially at rest and is discharged at the top of the sand mover with speed 5.0 m/s into a loading chute.What minimum power must be supplied to this machine?

To what radius would the sun have to be compressed in order for it to become a black hole? The mass of the sun is 1.99 × 10³⁰ kg,G = 6.67 × 10^-11 N ∙ m²/kg²,and c = 3.00 × 10⁸ m/s

In a police ballistics test,a 2.00-g bullet suddenly hits and becomes embedded in a 5.00-kg wood block which is hanging from a 1.20-m long string.This causes the block to swing through an arc of 3.50°.What was the speed of the bullet just before it hit the block?

Two men,Joel and Jerry,push against a car that has stalled,trying unsuccessfully to get it moving.Jerry stops after 10 min,while Joel is able to push for 5.0 min longer.Compare the work they do on the car.

Person X pushes twice as hard against a stationary brick wall as person Y.Which one of the following statements is correct?

A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface.They both slide up the same frictionless hill with no air resistance.Which object rises to a greater height?

A heavy stone and a light stone are released from rest in such a way that the amount of gravitational potential energy of the system rock-Earth for each rock is the same just as they are released.Air resistance is negligibly small.Which of the following statements about these stones are correct? (There could be more than one correct choice.)

It requires 0.30 kJ of work to fully drive a stake into the ground.If the average resistive force on the stake by the ground is $828 \mathrm {~N} \text {, }$ how long is the stake?

An 8.0-g bullet is suddenly shot into a 4.0-kg block,at rest on a frictionless horizontal surface,as shown in the figure.The bullet remains lodged in the block.The block then moves against a spring and compresses it by 8.9 cm.The force constant (spring constant)of the spring is $1400 \mathrm {~N} / \mathrm { m }$ What is the magnitude of the impulse on the block (including the bullet inside)due to the spring during the entire time interval during which the block compresses the spring?

A stone initially moving at 8.0 m/s on a level surface comes to rest due to friction after it travels 11 m.What is the coefficient of kinetic friction between the stone and the surface?

As shown in the figure,a bullet of mass 0.010 kg moving horizontally suddenly strikes a block of wood of mass 1.5 kg that is suspended as a pendulum.The bullet lodges in the wood,and together they swing upward a vertical distance of 0.40 m.The length of the string is 2.0 m.What was the speed of the bullet just before it struck the wooden block?

A traveler pulls on a suitcase strap at an angle 36° above the horizontal.The suitcase is the system.If $555 \mathrm {~J}$ of work are done by the strap while moving the suitcase a horizontal distance of $15 \mathrm {~m}$ what is the tension force that the strap exerts on the suitcase?

If a spring-operated gun can shoot a pellet to a maximum height of 100 m on Earth,how high could the pellet rise if fired on the Moon,where g = 1.6 m/s²?

Two objects of different masses have momentum of equal,non-zero magnitude.Which object has more kinetic energy?

Two cyclists who weigh the same and have identical bicycles ride up the same mountain,both starting at the same time.Joe rides straight up the mountain,and Bob rides up the longer road that has a lower grade.Joe gets to the top before Bob.Ignoring friction and wind resistance,which one of the following statements is true?