Relative motion questions can be found here and are shown below: Projectile Motion
A projectile is an object that once launched continues to move without assistance and only under that influence of gravity. Independence of Horizontal and Vertical Motion. An object launched with some initial horizontal velocity will fall at the same rate as one without any horizontal velocity and the two objects will hit the ground at the same time. This idea is know as the independence of horizontal and vertical motion. The horizontal velocity does not affect the vertical velocity in any way and conversely the vertical acceleration does not affect the horizontal velocity. Ignoring air-resistance we find: 1. The horizontal component of velocity remains constant (because the acceleration in the horizontal direction is zero since there is no component of force acting in the horizontal direction) 2. The vertical component of velocity continues to change with a constant acceleration (due to gravity) NB When solving projectile motion problems we must CONSIDER HORIZONTAL AND VERTICAL MOTION SEPARATELY A projectile with initial horizontal velocity Example: A ball is thrown from the top of a 15 m building with an initial speed of 3 m/s in the horizontal direction. Calculate: a) the time it takes for the ball to hit the ground; b) the distance from the base of the building that the ball lands. a) To work out the time we will consider vertical motion: in the vertical direction we know, u = 0m/s; a = 9.8 m/s^2; s = 15m; and we want to know t. Therefore we select the equation s = ut + 1/2 at^2. Since u = 0: s = 1/2 at^2 Substituting the values into the equation we find that t = sqrt(2s/a) = 1.75 s b) To work out the distance the ball lands from the base of the building we need to consider horizontal motion: We know the time it takes for the ball to hit the ground and we know the horizontal speed (which remains constant throughout) so we can simply do: distance = speed x time = 3 x 1.75 = 5.25 m Leave a Reply. |
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