单选题 A sphere is dropped near the surface of Earth. While falling, the sphere reaches terminal velocity. Which of the following sets of graphs correctly shows the magnitudes of the position $$y$$, velocity $$v$$, and acceleration $$a$$ of the sphere as functions of time $$t$$ as the sphere is falling?

A、

B、

C、

D、

下载APP答题
由4l***aa提供 分享 举报 纠错

相关试题

单选题 b88a256cd15429260589ae290d22312a.png

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 $$t = t_1$$?

A、$$A\left(\frac{t_1^3}{3}\right) - L_0$$
B、$$A\left(\frac{t_1^3 - t_0^3}{3}\right) + L_0$$
C、$$AR\left(\frac{t_1^3 - t_0^3}{3}\right)$$
D、$$AR\left(\frac{t_1^3 - t_0^3}{3}\right) + L_0$$

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?

A、0.11 J
B、0.90 J
C、1.0 J
D、1.9 J

单选题 0a9a99c8720091f0e97ad423fc3a4f55.png

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?

A、$$x = 4.0 - 0.57t$$
B、$$x = -4.0t + 1.15t^2$$
C、$$x = 4.0 - 1.15t$$
D、$$x = -1.5 + 4.0t - 0.57t^2$$

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?

A、2 m/s
B、6 m/s
C、10 m/s
D、14 m/s

单选题 6d1cb73013e0fca94a942d086a765ab5.png

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 $$90^\circ$$?

A、

$$F_1$$ Increases,

$$F_2$$ Increases

B、

$$F_1$$ Decreases,

$$F_2$$ Increases

C、

$$F_1$$ Increases,

$$F_2$$ Decreases

D、

$$F_1$$ Remains constant,

$$F_2$$ Increases

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?

A、$$F_N > F_g$$ because the person is moving upward.
B、$$F_N > F_g$$ because the person is accelerating upward.
C、$$F_N = F_g$$ because the forces are a Newton's third law action-reaction pair.
D、$$F_N = F_g$$ because the force of gravity and the normal force acting on an object are always equal.

单选题 2bd7d0336b6c007a9903781c45de31db.png

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 $$v_2$$?

A、$$v_1 > v_2$$
B、$$v_1 = v_2$$
C、$$v_1 < v_2$$
D、The speeds cannot be compared without knowing the angles of incline for the ramp.

单选题 9dcebb3af213d8d0425d30a205dbda4a.png

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?

A、The boxes move together to the left with the same acceleration.
B、The boxes move together to the right with the same acceleration.
C、The boxes move together to the left with the same constant speed.
D、The boxes move together to the right with the same constant speed.