0/20. Mon Nov :15 PM EST. Question Points. 0/20/20/20/10/10/20/10/30/20/20/2 Total 0/20. Description

Transcription

1 1 of 6 10/20/2009 3:20 PM 0/20 Mon Nov :15 PM EST Question Points /20/20/20/10/10/20/10/30/20/20/2 Total 0/20 Description This assignment is worth 20 points. Each part is worth 1 point. Assume the numbers given in each problem are accurate to three significant figures. WebAssign expects your answers to be accurate within 1%. If you don't round off until the end, and then round off to three significant figures, you should be fine. Occasionally there are errors in WebAssign. If you are convinced your answer is correct and WebAssign is grading you incorrectly please check with Professor Duffy. 1. 0/2 pointsduffy_ep_ch07_p30 [ ] As shown in the figure above, a wooden ball with a mass of 230 g swings back and forth on a string, pendulum style, reaching maximum speed of 4.00 m/s when it passes through its equilibrium position. Use g = 10.0 m/s 2. (a) At what maximum height above the equilibrium position was the ball released from rest? 0.8 m b) At one instant, when the ball is at its equilibrium position and moving left at 4.00 m/s, it is struck by a bullet with a mass of 0.0 g. This is shown in the figure. Before the collision, the bullet has a velocity of 293 m/s to the right. The bullet passes hrough the ball and emerges with a velocity of 100 m/s to the right. What is the magnitude and direction of the ball s velocity mmediately after the collision? To indicate the direction, use a positive sign if the ball's velocity is to the right, and a negative ign if the ball's velocity is to the left. Neglect any change in mass for the ball m/s. 0/2 pointsduffy_ep_ch07_p49ish [ ]

2 2 of 6 10/20/2009 3:20 PM A block of mass m is released from rest, at a height h = 4R above the base of a frictionless loop-the-loop track, as shown in he figure. The loop has a radius R = 50.0 cm. Use g = 10.0 m/s 2, to make the calculations easier. (a) What is the speed of the block when it reaches position b, shown in the figure? 4.47 m/s b) If the block has a mass of 100 g, calculate the magnitude of the normal force acting on the block when the block is at point. 3 N 3. 0/2 pointsduffy_ep_ch07_p58b [ ] A wooden block with a mass of 210 g rests on two supports. A piece of sticky chewing gum with a mass of 40.0 g is fired traight up at the block, colliding with the block when the gum s speed is 13.0 m/s. The gum sticks to the block. Use g = 10.0 /s 2. a) What is the speed of the gum-block system immediately after the collision? 2.08 m/s b) What is the maximum height reached by the gum-block system, measured from the point of the collision? m. 0/1 pointsduffy_ep_ch10_p20 [ ] An electric drill accelerates a drill bit, which has a radius of 3.00 mm, from rest to a maximum angular speed of 290 rpm revolutions per minute) in 2.30 seconds. Assuming that the drill bit s angular acceleration is constant, what is the magnitude f that angular acceleration? 13.2 rad/s. 0/1 pointsduffy_ep_ch10_p14 [ ] ou release a ball from rest at the top of a ramp, and it experiences a constant angular acceleration of 1.00 rad/s 2. At the bottom of the ramp, the ball is rotating at 6.00 revolutions per second. How long did it take the ball to travel down the ramp? 37.7 s. 0/2 pointsduffy_ep_ch10_p28 [ ]

3 3 of 6 10/20/2009 3:20 PM A solid sphere has a mass of M = 7.00 kg and a radius of R = 30.0 cm. (a) Determine the sphere s rotational inertia about an axis passing through the center of the sphere kg m 2 (b) Determine the sphere s rotational inertia about an axis that is tangent to the outer surface of the sphere kg m /1 pointsduffy_ep_ch10_p42 [ ] n the old days, long before CD s and MP3 s, people listened to music using vinyl records. Long-playing vinyl records spin at constant rate of 33-and-one-third rpm (revolutions per minute). The music is encoded onto a continuous spiral track on the ecord that starts at a radius of 30 cm from the center and ends at a radius of 10 cm from the center. If a record plays for 24 inutes, how far apart are the grooves in the track on the record? cm. 0/3 pointsduffy_ep_ch10_p09 [ ] You construct a mobile out of four objects, a sphere, a pyramid, an ellipsoid, and a cube. The mobile is in equilibrium in the configuration shown above, where the vertical dashed lines are 20 cm apart. The mass of the strings (in blue) and rods (in red) can be neglected. If the pyramid has a mass of 360 g, what is the mass of each of the other objects? See if you can do this problem without a calculator. (a) What is the mass of the ellipsoid? 90 g b) What is the mass of the cube? 270 g c) What is the mass of the sphere? 1080 g. 0/2 pointsduffy_ep_ch10_p60ish [ ] ou are using a wheelbarrow to move a heavy rock, as shown in the figure below. The diagram shows the location of the pward force you exert and the location of the force of gravity acting on the rock-wheelbarrow system.

4 4 of 6 10/20/2009 3:20 PM (a) If the force of gravity on the rock-wheelbarrow system has a magnitude of 480 N, solve for the magnitude of the force, F, that you exert on the wheelbarrow. 80 N b) What is the magnitude of the normal force exerted on the wheel of the wheelbarrow by the ground? The wheel is the only art of the wheelbarrow in contact with the ground in this situation. 400 N 10. 0/2 pointswiley Simulation [206957] Rotational Equilibrium (a) Given the limits on the sliders available to you in the simulation, what is the maximum value the blue support force can be? 150 N b) Which of the following statements about this situation are true? Select all that apply. Consider these statements in terms of hat can be achieved in the simulation, thinking carefully about the limits on the various sliders. The beam will be less likely to tip if the red support is moved to the left end and the blue support is moved to the right end. Moving a box away from

5 5 of 6 10/20/2009 3:20 PM a support always decreases the force applied on the beam by that support. If the beam starts at rest, the beam remains at rest, in static equilibrium, as long as the net force is zero or the net torque is zero. Static equilibrium does not require that both of these conditions be met. The system's centerof-gravity (shown as a white + on the free-body diagram) is always halfway between the two supports. Increasing the weight of the beam generally makes the system more stable (less likely to tip). Given the limits set by the sliders in the simulation it is not possible for the system to tip over. The system will always be stable if both boxes are between the two supports. The system will always tip over if both boxes are placed either to the left of both supports or to the right of both supports /2 pointsduffy_ep_ch10_p54 [ ]

6 6 of 6 10/20/2009 3:20 PM It is often useful to treat the lower arm as a uniform rod of length L and mass M = 1.50 kg that can rotate about the elbow. et s say you are holding your arm so your upper arm is vertical (with your elbow below your shoulder), with a 90-degree bend t the elbow so the lower arm is horizontal. In this position, we can say that three forces act on your lower arm: the force of ravity (Mg), the force exerted by the biceps, and the force exerted at the elbow joint by the humerus (the bone in the upper rm). Let s say the biceps muscle is attached to the lower arm at a distance of L/10 from the elbow, moving away from the lbow toward the hand. Use g = 10 m/s 2. a) Assuming that the force the biceps muscle exerts on the lower arm is vertical, what is the magnitude of the biceps force? 75 N b) Determine the force that the humerus exerts on the lower arm. If this force is directed up, use a positive sign. If this force is irected down, use a negative sign. -60 N Assignment Details