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A pebble of mass 0.05 kg is thrown vertically upwards. Give the direction and magnitude of the net force on the pebble. [Ignore air resistance] a) during its upward motion b) during its downward motion c) at the highest point where it is momentarily at rest. Do your answers change if the pebble was thrown at an angle of 45° with the horizontal direction? |
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Answer» Solution :When a body is thrown vertically upwards (or) it moves vertically downwards, gravitational PULL of earth gives it a uniform acceleration `a = +g = +9.8 ms^(-2)`in the DOWNWARD DIRECTION. Therefore, the net force on the pebble in all the three cases is vertically downwards. As m = 0.05 kg and `a = + 9.8 m//s^(2)` `therefore` In all the three case, `F = ma = 0.05^(@) 9.8 = 0.49N`. Vertically downwards. If the pebble were thrown at an angle of 45° with the HORIZONTAL direction, it will have horizontal and vertical components of velocity. These components do not affect the force on the pebble. Hence our answers do not alter in any case. HOWEVER in each case (C), the pebble will not be at rest. It will have horizontal component of velocity at highest point. |
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