physics

If the potential energy function if given by U(r)=br^-3/2+c, where b and c are constants, which of the following is an expression for the force on the particle.

(3b/2)r^-5/2

A system consists of two objects having masses m1 and m2 (m1<m2). The objects are connected by a massless string, ung over a pulley as shown above, and then released. When the object of mass m2 has descended a distance h, the potential energy of the system has decreased by A. (M2-M1)gh B. m2GH C (M1+M2)gh D. .5(M1+m2)gh E. 0

(m2-m1)gh

When a block slides a certain distance down an incline, the work done by gravity is 300 J. What is the work done by gravity of this block slides the same distance up the incline?

-300 J

A disc of mass m slides with negligible friction along a flat surface with a velocity v. The disc strikes a wall head-on and bounces back in the opposite direction with a kinetic energy one-fourth of its initial kinetic energy. What is the final velocity of the disc

-v/2

A spring has a force constant of 100 N/m and an unstretched length of 0.07 m. One end is attached to a post that is free to rotate in the center of a smooth table, as shown in the top view above. The other end is attached to a 1 kg disc moving in uniform circular motion on the table, which stretches the spring by 0.03 m. Friction is negligible. What is the work done on the disc by the spring during one full circle?

0 J

A student holds one end of a string in a fixed position. A bell of mass 0.2 kg attached to the other end of the string moves in a horizontal circle of radius 0.5m with a constant speed of 5 m/s. How much work is done on the ball by the string during each revolution?

0 J

for a particular nonlinear spring, the relationship between the magnitude of the applied force F and the resultant displacement x from equilibrium is given by the equation F=kx^2. What is the amount of work done by stretching the spring a distance x0?

1/3kx0^3

A 1000 W electric motor lifts a 100 kg safe at constant velocity. The vertical distance through which the motor can raise the safe in 10 s is most nearly

10 m

During a certain time interval, a constant force delivers an average power of 4 watts to an object. If the object has an average speed of 2 meters per second and the force acts in the direction of motion of the object, the magnitude of the force is

2 N

A ball is thrown upward. At a height of 10 meters above the ground, the ball has a potential energy of 50 joules (with the potential energy equal to zero at ground level) and is moving upward with a kinetic energy of 50 joules. Air friction is negligible. The maximum height reached by the ball is most nearly

20 m

From the top of a 70-meter-high building, a 1-kilogram ball is thrown directly downward with an initial speed of 10 meters per second. If the ball reaches the ground with a speed of 30 meters per second, the energy lost to friction is most nearly

300 J

A 10-kilogram body is constrained to move along the x-axis. The potential energy in joules is given as a function of its position x in meters by U(x)=6x^2-4x+3. The force on the particle at x=3 meters is

32 N in -x direction

A descending elevator of mass 1,000 kg is uniformly decelerated to rest over a distance of 8m by a capable in which the tension is 11,000 N. The speed vi of the elevator at the beginning of the 8 m descent is most nearly

4 m/s

A person pushes a box across a box across a horizontal surface at a constant speed of 0.5 meter per second. The box has a mass of 40 kilograms, and the coefficient of sliding friction is 0.25. The power supplied to the box by the person is

50 W

A frictionless pendulum of length 3 m swings with an amplitude of 10 degrees. At its maximum displacement, the potential energy of the pendulum is 10 J. What is the kinetic energy of the pendulum when its potential energy is 5J.

5J

A 2000 kg car, initially at rest, is accelerated along a horizontal roadway at 3 m/s^2. What is the average power required to bring the car to a final speed of 20 m/s

6 x 10^4 W

To stretch a certain nonlinear spring by an amount x requires a force F given by F=40x-6x^2, where F is in newtons and x is in meters. What is the change in potential energy when the spring is stretched 2 meters from its equilibrium position?

64 J

the following graphs, all drawn to the same scale, represent the net force F as a function of displacement x for an object that moves along a straight line. Which graph represents the force that will cause the greatest change in kinetic energy of the object from x=0 to x=x1

E, graph with greatest area under curve

A force F is exerted by a broom handle on the head of the broom, which has a mass m. The handle is at an angle theta to the horizontal, as shown above. The work done by the force on the head of the broom as it moves a distance d across a horizontal floor is

Fdcostheta

A conservative force has the potential energy function U(x), shown by the graph above. A particle moving in one dimension under the influence of this force has kinetic energy 1.0 joule when it is at position x1. Which of the following is a correct statement about the motion of the particle

it cannot reach either x0 or x2

All of the following are units of power EXCEPT

kilogram meters per second

an object of mass m is lifted at constant velocity a vertical distance H in time T. The power supplied by the lifting force A. mgHT B.mgH/t C. mg/HT D. mgT/H E. Zero

mgH/T

A weight lifter lifts a mass m at constant speed to a height h in time t. How much work is done by the weight lifter?

mgh

If the particle is released from rest at position r0, its speed at position 2r0 is most nearly

sqrt(4U0/m)

A pendulum consists of a ball of mass m suspended at the end of a massless cord of length L as shown above. The pendulum is drawn aside through an angle of 60 degrees with the vertical and released. At the low point of its swing, the speed of the pendulum ball is

sqrt(gL)

If a particle moves in such a way that its position x is described as a function of time t by x=t^3/2, then its kinetic energy is proportional to A. t^2 B T^(3/2) C. t^1/2 E. t^0, KE is constant.

t

when an object is moved from rest at point A to rest at point B in a gravitational field, the net work done by the field depends on the mass of the object and

the positions of A and B only

a rock is lifted for a certain time by a force F that is greater in magnitude than the rock's weight W. The change in kinetic energy of the rock during this time is equal to the

work done by the net force (F-W)