Chapter 7-9 physics

A potential energy function for system 1 is given by U1(x) = Cx2 + Bx3. The potential energy function for system 2 is given by U2(x) = A + Cx2 + Bx3, where A is a positive quantity. How does the force on system 1 relate to the force on system 2 at a given position?

The force is identical on the two systems

Two identical balls are thrown directly upward, ball A at speed v and ball B at speed 2v, and they feel no air resistance. Which statement about these balls is correct?

) Ball B will go four times as high as ball A because it had four times the initial kinetic energy

A 2-kg mass traveling at 1.8 m/s has a kinetic energy of

3.24 J

The work done by friction, f,

equals -fd, where d is the total distance moved.

A 2.0 gram bead slides along a frictionless wire, as shown in the figure. At point A, the bead is moving to the right (positive x direction) but with negligible speed. What is the speed of the bead at point C?

+2.0 m/s (Since the wire is frictionless, gravity is the only force doing work. Gravity is a conservative force thus the total mechanical energy at points A and C is the same.)

In the figure, a toy racecar of mass m, with very light wheels is released from rest on the loop-the- loop track. If it is released at a height 2R above the floor, how high is it above the floor when it leaves the track? Neglect any type of friction in this problem.

1.67 R

How fast would a 100-kg meteorite have to travel to have the same energy as a 10,000-kg meteorite traveling at 100 m/s?

1000 m/s

A 102-kg man climbs a 5.0-meter-high staircase at constant speed. How much work does he do?

5000 J

Which does more work, a force of 89 N acting at an angle of 89o or a force of 1 N acting at an angle of 1o?

89 N

Which, if any, of the following statements concerning the work done by a conservative force is NOT true?

All of the above statements are true

Two stones, one of mass m and the other of mass 2m, are thrown directly upward with the same velocity at the same time from ground level and feel no air resistance. Which statement about these stones is true?

At its highest point, the heavier stone will have twice as much gravitational potential energy as the lighter one because it is twice as heavy.

Block 1 and block 2 have the same mass, m, and are released from the top of two inclined planes of the same height making 30° and 60° angles with the horizontal direction, respectively. If the coefficient of friction is the same in both cases, which of the blocks is going faster when it reaches the bottom of its respective incline?

Block 2 is faster.

Block 1 and block 2, each of mass, m are released from the top of two inclined planes of the same height making 30° and 60° angles with the horizontal direction, respectively. If the coefficient of friction is the same in both cases, which of the blocks is going faster when it reaches the bottom of its respective incline?

Block 2 is faster.

In a collision between two objects having unequal masses, how does the magnitude of the impulse imparted to the lighter object by the heavier one compare with the magnitude of the impulse imparted to the heavier object by the lighter one?

Both objects receive the same impulse.

Which exerts more work, a 50-kg student climbing a 10-m-high staircase at constant speed in 2 seconds or a 100-kg student climbing the same staircase in 4 seconds?

The 100-kg student

A 4-kg mass moving with speed 2 m/s and an otherwise identical 2-kg mass moving with a speed of 4 m/s are gliding over a horizontal surface with friction, and are brought to rest by it. Which statement best describes their respective stopping distances?

The 2-kg mass travels greater than twice as far.

A 4-kg mass moving with speed 2 m/s and a 2-kg mass moving with a speed of 4 m/s are gliding over a horizontal frictionless surface. Both objects encounter the same horizontal force which directly opposes their motion, and are brought to rest by it. Which statement best describes their respective stopping distances?

The 2-kg mass travels twice as far as the 4-kg mass before stopping.

Which has more energy, a 1000-kg car traveling at 1 cm/s or a 1-gm bullet traveling at 1000 m/s?

The bullet.

Is it possible for a system to have negative potential energy?

Yes, since the choice of the zero of potential energy is arbitrary.

In the figure, a graph of potential energy U versus position x for a particle moving in a straight line is shown. For the region shown, it is true that

The force on the particle would be strongest when the particle is near the origin. (the magnitude of the force is proportional to the slope of the U curve. U is steepest near the origin.)

Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height?

The two objects rise to the same height.

When an object is solely under the influence of conservative forces, the sum of its kinetic and potential energies does not change

True

A ball drops some distance and loses 30 J of gravitational potential energy. Do NOT ignore air resistance. How much kinetic energy did the ball gain?

less than 30 J

A ball drops some distance and gains 30 J of kinetic energy. Do NOT ignore air resistance. How much gravitational potential energy did the ball lose?

more than 30 J

A box of mass m is pressed against (but is not attached to) an ideal spring of force constant k and negligible mass, compressing the spring a distance x. After it is released, the box slides up a frictionless incline as shown in the figure and eventually stops. If we repeat this experiment with a box of mass 2m

the lighter box will go twice as high up the incline as the heavier box.

The resultant force you exert on a shopping cart for a 10-second period is plotted on the graph shown. How much work did you do during this 10-second interval?

zero

What was the total work done on you by all the forces in the universe between the time just before you awoke this morning and right now?

zero