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Unformatted text preview: homework 08 – ARMSTRONG, DOMINIC – Due: Oct 30 2007, 3:00 am 1 Question 1, chap 11, sect 1. part 1 of 1 10 points The graph below shows the force on an object of mass M as a function of time. Time (s) Force(N) 1 2 3 4 10- 10 For the time interval 0 to 4 s, the total change in the momentum of the object is 1. Indeterminable unless the mass M of the object is known 2. Δ p = 40 kg m / s . 3. Δ p = 0 kg m / s . correct 4. Δ p =- 20 kg m / s . 5. Δ p = 20 kg m / s . Explanation: The Newton’s second law of motion, in one dimension, is F = M a = M dv dt . From this, we obtain F dt = M dv , = ⇒ Δ( M v ) = integraldisplay F dt, where M v is the momen- tum of the object. So from the graph above, the change in the momentum is zero . Question 2, chap 11, sect 1. part 1 of 1 10 points A constant force is exerted for a short time interval on a cart that is initially at rest on an air track. This force gives the cart a certain final speed. Suppose we repeat the experiment but, instead of starting from rest, the cart is already moving with constant speed in the direction of the force at the moment we begin to apply the force. After we exert the same constant force for the same short time interval, the increase in the cart’s speed 1. cannot be determined from the informa- tion provided. 2. is equal to four times its initial speed. 3. is equal to two times its initial speed. 4. is equal to the square of its initial speed. 5. is the same as when it started from rest. correct Explanation: The increase in speed is proportional to both the force on the cart and the time over which it acts. Question 3, chap 11, sect 2. part 1 of 1 10 points Objects having the same mass travel toward each other on a flat surface, each with a speed of 1.0 meter per second relative to the surface. The objects collide head-on and are reported to rebound after the collision, each with a speed of 2.0 meters per second relative to the surface. Which of the following assessments of this report is most accurate? 1. Momentum was not conserved; therefore the report is false. 2. If potential energy were released to the objects during the collision, the report could be true. correct 3. If the surface were inclined, the report could be true....
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