1. The figure above shows a truck pulling three crates across a rough road. Which of the following shows the directions of all the horizontal forces acting on crate 2 ?
2. Two blocks are on a horizontal, frictionless surface. Block A is moving with an initial velocity of v0 toward block B, which is stationary, as shown above. The two blocks collide, stick together, and move off with a velocity of v0/3. Which block, if either,has the greater mass?
(A) Block A
(B) Block B
(C) Neither; their masses are the same.
(D) The answer cannot be determined without knowing the mass of one of the blocks
Questions 3 -5 refer to the following material.
A student sets an object attached to a spring into oscillatory motion and uses a motion detector to record the velocity of the object as a function of time. A portion of the recorded data is shown in the figure above.
3. The total change in the object’s speed between 1.0 s and 1.1 s is most nearly
(B) 5 cm / s
(C) 10 cm / s
(D) 15 cm / s
4. The acceleration of the object at time t=0.7s is most nearly equal to which of the following?
(A) The value of the graph where it crosses the 0.7 s grid line
(B) The slope of the line connecting the origin and the point where the graph crosses the 0.7 s grid line
(C) The area under the curve between where the graph crosses the time axis near 0.63 s and time 0.7 s
(D) The slope of the tangent to a best-fit sinusoidal curve at 0.7 s
5. The frequency of oscillation is most nearly
(A) 0.63 Hz
(B) 0.80 Hz
(C) 1.25 Hz
(D) 1.60 Hz
1. (7 points, suggested time 13 minutes)
A toy consists of two identical solid spheres connected by a string with negligible mass. The toy is thrown at an angle above the horizontal (not straight up) such that the string remains taut and both spheres are revolving counterclockwise in a vertical plane around the center of the string, as shown above.
(a) Sketch graphs of the horizontal and vertical components of the velocity of the center of the string as a function of time, from the instant the spheres are released at time t = 0 until the instant the system returns to its initial height at time tf. Take the positive direction to be toward the right for the horizontal component and the positive direction to be upward for the vertical component.
(b) The figure above shows the toy at the instant the center of the string reaches the top of its trajectory. This is a side view: the sphere on the left is higher than the sphere on the right.
i On the dot below, which represents the left sphere only, draw and label the forces (not components) exerted on the left sphere at this instant. Represent each force by a distinct arrow starting on, and pointing away from, the dot. The dashed line is drawn at the same angle as the string.
ⅱOn the dot below, which represents the whole toy(the spheres-string system), draw and label the forces (not components) that act on the system at this instant. Represent each force by a distinct arrow starting on, and pointing away from, the dot. The dashed line is drawn at the same angle as the string.
ⅲWhen the toy was released, the center of the string was moving with an initial speed of 15 m/s at a 60°angle above the horizontal. Calculate the speed of the center of the string at the instant shown above, when the center of the string reaches the top of its trajectory.