谁能帮我做下大写物理题啊？

2025-03-07 00:17:36

推荐回答（1个）

回答（1）：

Ⅰ. Multiple choices (there is one correct answer only):
1. The center of mass a system of particles has a constant velocity if:
A. the forces exerted by the particles on each other sum to zero.
B. the external forces acting on particles of the system sum to zero.
C. the velocity of the center of mass is initially zero.
D. the particles are distributed symmetrically around the center of mass.
E. the center of mass is at the geometric center of the system
.
2. A wheel starts from rest and has an angular acceleration that is given by α(t)=6t2, where t is in seconds and α is in radians per second-squared. The time it takes to make 10 rev（转） is:
A. 2.8s
B. 3.3s
C. 4.0s
D. 4.7s
E. 5.3s

3. A spool(线轴) of wire rests on a horizontal surface as in Figure. As the wire is pulled, the spool does not slip at the contact point P. On separate trials, each one of the forces F1, F2, F3, and F4 is applied to the spool. Among these 4 forces, which one can make the spool roll in clockwise? (Note that the line of action of F2 passes through P.)

A. F1
B. F2
C. F3
D. F4
E. none of the above

4. A pulley with radius R and rotational inertia I is free to rotate on a horizontal fixed axis through its center. A string passes over the pulley. Mass m1 is attached to one end and mass m2 is attached to the other. At one time m1 is moving downward with speed v. If the string does not slip on the pulley, the magnitude of the total angular momentum, about the pulley center, of the masses and pulley, considered as a system, is given by:
A. (m1- m2)vR+Iv/R
B. (m1+ m2)vR+Iv/R
C. (m1- m2)vR-Iv/R
D. (m1+ m2)vR-Iv/R
E. none of the above

5. An ideal spring, with a pointer attached to its end, hangs next to a scale. With a 100-N weight attached and at rest, the pointer indicates “40” on the scale as shown. Using a 200-N weight instead results in “60” on the scale. Using an unknown weight X instead results in “30” on the scale. The weight of X is:
A. 10N
B. 20N
C. 30N
D. 40N
E. 50N

6. The potential energy for a body of mass m that is acted on by a very massive body is given by U=-mgx+kx2/2. The corresponding force is:
A. –mgx2/2+kx3/6.
B. mgx2/2-kx3/6.
C. –mg+kx/2
D. –mg+kx
E. mg-kx

7. Two particles, each of mass m, are a distance d apart. To bring a third particle, also with mass m, from far away to the point midway between the two particles an external force does work given by:
A. 4Gm2/d
B. -4Gm2/d
C. 4Gm2/d2
D. -4Gm2/d2
E. none of above

8. The displacement of a string carrying a traveling sinusoidal wave is given by y(x,t)=ymsin(kx-ωt-φ). At time t=0, the point at x=0 has a velocity of zero and a positive displacement. The phase constant φ is:
A. 45°
B. 90°
C. 135°
D. 180°
E. 270°

9. Two sinusoidal waves travel in the same direction and have the same frequency. Their amplitudes are y1m and y2m. The smallest possible amplitude of the resultant wave is:
A. y1m+ y2m and occurs when they are 180°out of phase
B. │y1m- y2m│and occurs when they are 180°out of phase
C. y1m+ y2m and occurs when they are in phase
D. │y1m- y2m│and occurs when they are in phase
E. │y1m- y2m│and occurs when they are 90°out of phase

10. Two sources, S1 and S2, each emit waves of wavelength λ in the same medium. The phase difference between the two waves, at the point P shown, is (2π/λ)(r2-r1)+φ. The quantity φ is:
A. the distance S1S2
B. the angle S1PS2
C. π/2
D. the phase difference between the two sources
E. zero for transverse waves, π for longitudinal waves

Ⅱ.Calculation problems (present the necessary equations in solution):
1、A bullet of mass m moving with velocity strikes and becomes embedded at the edge of a cylinder of mass M and radius R0, as shown in Fig. The cylinder, initially at rest, begins to rotate about its symmetry axis, which remains fixed in position. Assuming no frictional torque, what is the angular velocity of the cylinder after this collision? Is kinetic energy conserved?

2、As shown in Fig., a simple harmonic wave is traveling along the positive direction of X axis, the reflected point P is a node and and . Find: (1) the oscillation equation at position P caused by incidence wave; (2) the reflected wave equation; (3) the standing wave equation; (4) the resultant oscillation equation at position D.

3、How much work must be done to increase the speed of a particle with rest mass from rest to ( where is the speed of light in vacuum)?

4、 An observer A is at rest in the frame OXY while another observer B moves along the X-axis with a constant velocity 0.8c (c is the light speed in vacuum). In frame OXY the observer A find that the area enclosed by a geometric circle is 12 cm2. Relying on the relativistic effect of length contraction, this geometric figure becomes an ellipse for Observer B. What area is the ellipse enclosed measured by B? (It is known that the area of an ellipse with semimajor axis a （长半轴）and semiminor axis b （短半轴）can be calculated by Sab).

5、Figure shows a hypothetical speed distribution of N molecules in an ideal gas, with for and for . Find
(1) an expression for C in terms of N and ?
(2) the average speed of the particles:
(3) the rms speed of the particles?

6、A power plant generates 640 MW of electric power. It has an efficiency of 38% . At what rate does it dissipate heat? If a river carries the waste heat away, and environmental concerns limit the temperature rise of the water to 3oC, what mass flow rate(流量) is required in the river? (the specific heat capacity of water c=4200J/kgK)

7、One mole of a monatomic ideal gas initially at , is heated and expands at constant pressure to a volume 4V0. It is then cooled at constant volume until the pressure has dropped to 0.5 . Calculate (a) the work done: (b) the change in internal energy, (c) the heat flow, and (d) the net change in entropy.

8、An ideal(Carnot) engine operates between a hot reservoir at 360K and a cold reservoir at 270K. It absorbs 600J of heat per cycle at the hot reservoir. (a) How much work does it do each cycle? (b) If the same engine is operated in reverse as a refrigerator, how much work must be done each cycle in order to remove 1200J of heat from the cold reservoir each cycle? (c) An engine manufacturer makes the following claims: The heat input per cycle of the engine is 600J at 360K. The heat output per cycle is 420J at 270K. Do you believe these claims? Why?

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