Class:11 Gravitation. 1.Why the value of g is more at the poles than t the equator? As g=(GM/R2) and the value of R at equator is greater than that at poles, hence g at poles is greater than g at equator. 2.Why a body weighs more at the poles than at the equator? This is because gp>ge and hence mgp >mge. Thus, a body weighs more at the poles than at the equator. 3.Where will a lady weigh more -1km above the surface of earth or 1Km below the surface of earth? The acceleration due to gravity (g) is given by .. g1 = (1- -h/R) above the earth’s surface. …g2 = (1--2h/R) below earth’s surface. These relations tells us that g2>g1 so the body will weigh more at a depth of 1km below the surface of earth. 4.What will be our weight at the center of earth, if the earth were a hollow sphere? The acceleration due to gravity is g1 = (1- -h/R) below earth’s surface. At the center of the earth h=R so g’ = 0. So our weight = mg’ =mx0=0. A body of mass 5Kg is taken to the centre of the earth. What will be its mass there? Mass of the body will remain 5kg at the centre of the earth because mass of a body does not depend on place. 5.Why does a tennis ball bounce higher on a hill than on planes? The value of g is less on hills because they are comparatively at a greater distance from the centre of the earth. Therefore, the gravitational pull on the tennis ball is less on hill tops and so it bounces higher on hills than on planes. 6.Why is it difficult to catch a cricket ball than to catch a tennis ball? This is because of heavier of cricket ball than tennis ball. During motion the cricket ball attains more momentum and therefore it exerts more force on hands when it is caught. 7.Why do you feel giddy (dizziness) while moving on a merry-go-round? When moving in a merry-go-round, our weight appears to decrease when we move down and appear to increase when we move we move up. Due to increase and decrease in eight during moving a merry-go=round, we feel giddy. 8.When dropped from the same height a body reaches the ground quicker at poles than at the equator. Why? The acceleration due to gravity is more at the poles than at the equator. When the initial velocities and distances travelled are the same, the time taken by the body is smaller if the acceleration due to gravity is large. Hence, when dropped from the same height, a body reaches the ground quicker at the poles than at the equator. 9.What is the time period of a simple pendulum at the centre of the earth? As g=0 at the centre of earth, so T= 2π√(l/g) = ∞. Hence, the pendulum will not vibrate at all. 10.When a train moves from west to east at high speed, does its weight increase or decrease? The weight decreases. This is because the apparent acceleration due to gravity is given by G’ = g- ω2R cos2θ As a train moves from west to east the term (ω2R cos2θ), which comes due to the rotation of a body about the axis of rotation of the earth, increases and therefore, g’ decreases and consequently, apparently weight mg’ decreases. 11.What is the effect on our weight due to revolution of the earth about the sun? There is no any factor involved in the expression of g which is influenced by the revolution of the earth about the sun so we can say that no effect is on our weight due to revolution of the earth about the sun.
Posted on: Mon, 08 Dec 2014 16:28:05 +0000