A radio transmission tower of mass m and length l is anchored to the ground by a
ID: 1304173 • Letter: A
Question
A radio transmission tower of mass m and length l is anchored to the ground by a flexible joint at its base (labeled P in the figure below), but is secured by cables. When the cables break and a blowing wind tips it to the right, however, (see figure) it, falls to the ground with an ever-increasing magnitude of angular velocity d theta /dt, as shown in the figure. Which of the following statements is true at any instant during this fall (Explain your reasoning). The torque about point P due to gravity is given by mgl/2 cos theta pointing out of the paper. The torque about point P due to gravity is given by mg l/2, cos theta pointing away from P along the tower. The torque about point P due to gravity is given by mg l/2 sin theta pointing into the paper. The torque about point P due to gravity is given by mg l/2 sin theta pointing out of the paper. A truck going 15 km/h has a head-on collision with a small car going 30 km/h. Which of the following statements best describes the situation. (Explain your reasoning using Newton's third law and conservation of linear momentum). The truck has the greater change of momentum because it has the greater mass. The car has the greater change of momentum because it has the greater speed. Neither the car nor the truck change their momentum because momentum is conserved. They both have the same change in magnitude of momentum because momentum is conserved.Explanation / Answer
1] c] we apply torque = r* F = l/2 sin[@]* mg = mgl/2sin[@] pointing into the plane of the paper
2]d] they both have the same change in momentum as the momentum is conserved