相关试题
单选题 A disk of mass $$M$$ and radius $$R$$ is rotating clockwise about its center. At time $$t = t_0$$, the disk has angular momentum $$L_0$$ and a force is applied tangent to the edge of the disk, as shown in the top view. The magnitude of the force is modeled by $$F(t) = At^2$$, where $$A$$ is a positive constant with appropriate units. What is the magnitude of the angular momentum of the disk at a later time $$t = t_1$$? 
单选题 A 0.9 kg cart is at position $$x = 0$$ and moves with initial velocity 1.5 m/s. A force exerted on the cart is given by $$F(x) = (2.0 \, \text{N/m}^3)x^3 + (1.2 \, \text{N/m}^2)x^2$$, where $$x$$ is the position of the cart. What is the change in kinetic energy of the cart when the cart has moved from $$x = 0$$ to position $$x = 1.0$$ m?
单选题 The graph shows the velocity as a function of time for an object moving along the x-axis. Which of the following equations could correctly represent the motion of the object? 
单选题 A car traveling at 20 m/s along a straight road passes a road sign at time $$t = 0$$. At time $$t = 1$$ s, the car accelerates at $$-6 \, \text{m/s}^2$$. Which of the following is closest to the speed of the car after it has traveled 50 m past the road sign?
单选题 Three forces are exerted on an object in equilibrium, as shown. The magnitudes of $$F_1$$ and $$F_2$$ and the angle $$\theta$$ can be changed. The magnitude of $$F_3$$ remains constant. Which of the following changes, if any, to $$F_1$$ and $$F_2$$ would keep the object in equilibrium as $$\theta$$ increases to $$90^\circ$$? 
单选题 A person jumps vertically upward. The floor exerts a force $$F_N$$ on the person, and Earth exerts a force $$F_g$$ on the person. Which of the following correctly compares $$F_N$$ and $$F_g$$ while the person is in contact with the floor and accelerating upward?
单选题 A block is pushed from rest by a force of magnitude $$F$$ a distance $$L$$ along an inclined ramp, as shown in Figure 1. The block leaves the end of the ramp and reaches the ground to the right of the ramp with speed $$v_1$$. The ramp is now raised to a greater angle with the horizontal, and the block is again pushed from rest by a force of magnitude $$F$$ a distance $$L$$, as shown in Figure 2. The block leaves the end of the ramp and reaches the ground to the right of the ramp with speed $$v_2$$. Frictional forces are negligible. Which of the following correctly compares $$v_1$$ and $$v_2$$? 
单选题 Box 1 is in contact with the ground and Box 2 on top of Box 1. Boxes 1 and 2 are initially at rest, as shown in Figure 1. An external force is then exerted on Box 1. Figure 2 shows the free-body diagram for Box 2 while the external force is exerted on Box 1. The forces exerted on Box 1 are not shown. Which of the following could describe the motion of the boxes? 