Gravitation 2 PDF Physics Past Paper

5.3-2 Gravitation and the Principle of Superposition Example Summing two forces: Figure 13-4 © 2014 John Wiley & Sons, Inc. All rights reserved. 5.3-2 Gravitation and the Principle of Superposition Answer: (a) 1, 2 & 4, 3 (b) line of length d © 20...

5.3-2 Gravitation and the Principle of Superposition Example Summing two forces: Figure 13-4 © 2014 John Wiley & Sons, Inc. All rights reserved. 5.3-2 Gravitation and the Principle of Superposition Answer: (a) 1, 2 & 4, 3 (b) line of length d © 2014 John Wiley & Sons, Inc. All rights reserved. 5.3-3 Gravitation Near Earth's Surface Learning Objectives 13.06 Distinguish between the 13.07 Calculate the free-fall acceleration and the gravitational acceleration gravitational acceleration. near but outside a uniform, spherical astronomical body. Lift, free-fall; centripetal acceleration; weightlessness 13.08 Distinguish between measured weight and the magnitude of the gravitational force.. © 2014 John Wiley & Sons, Inc. All rights reserved. 5.3-3 Gravitation Near Earth's Surface Combine F = GMm/r2 and F = mag: Eq. (13-11) This gives the magnitude of the gravitational acceleration at a given distance from the centre of the Earth Table 13-1 shows the value for ag for various altitudes above the Earth’s surface Table 13-1 © 2014 John Wiley & Sons, Inc. All rights reserved. 5.3-3 Gravitation Near Earth's Surface The calculated ag will differ slightly from the measured g at any location Therefore the calculated gravitational force on an object will not match its weight for the same 3 reasons: 1. Earth's mass is not uniformly distributed, Fig. 13-5 2. Earth is not a sphere 3. Earth rotates Figure © 2014 John Wiley 13-5 & Sons, Inc. All rights reserved. 5.3-3 Gravitation Near Earth's Surface Example Difference in gravitational force and weight due to rotation at the equator: Eq. (13-12) Eq. (13-14) Figure © 2014 John Wiley & Sons, Inc. All rights reserved. 13-6 5.3-3 Gravitation Near Earth's Surface Example Simulating weightlessness: imagine being on a platform moving with angular velocity ω at a distance R from the centre, such that ω2R = ag, then g = 0, hence mg=0 Eq. (13-12) Eq. (13-14) Figure © 2014 John Wiley & Sons, Inc. All rights reserved. 13-6  Weighing a Fish in an Elevator* *From College Physics, Serway, Example 4:9) Goal Explore the effect of acceleration on the apparent weight of an object Problem: A man weighs a fish with a spring scale attached to the ceiling of an elevator, as shown in the figure. While the elevator is at rest, he measures a weight of 40.0 N. (a) What weight does the scale read if the elevator accelerates upward at 2.00 m/s2? (b) What does the scale read if the elevator accelerates downward at 2.00 m/s2? (c) If the elevator cable breaks, what does the scale read? Strategy Write down Newton’s second law for the fish, including the force exerted by the spring scale and the force of gravity,. The scale doesn’t measure the true weight, it measures the force T that it exerts on the fish, so in each case solve for this force, which is the apparent weight as measured by the scale. Remarks Notice how important it is to have correct signs in this problem! Accelerations can increase or decrease the apparent weight of an object. Astronauts experience very large changes in apparent weight, from several times normal weight during ascent to weightlessness in free fall. You can apply similar analyses to determining the apparent weight of the man himself. That would be the Normal reaction from the floor where he stands. i.e. N takes the place of T in the above problem.