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1. Why does a tennis ball bounce higher on hills than on plains?
2. What is the maximum percentage error in the measurement of kinetic
energy if the percent errors in mass and velocity are 2% and 3%
respectively?
3. A thief jumps from the upper storey of a house with a load on his back.
What is the force of the load on his back when the thief is in air?
4. Why we cannot open or close a door by applying force at the hinges?
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Let's see the answers :
1) Hills have a sharpened top point with a very less area. Less the area, more the pressure and hence more will be the force exerted on the ball by the hill, and for this the ball bounce higher than on plains. A plain, being a flat surface, has a wide area (large area). More the area, less the pressure, and hence less the force for which it will exert less force on the surface of the ball and the ball will bounce comparatively less than hills.
3) Both the thief and load falls down with same acceleration due to gravity.As there is no relative motion between them, the load is considered to be in rest when compared to the thief. So, there is no possibility of force applied on the thief for zero relative acceleration between them.
Shortly, we can state it as Force is directly proportional to acceleration (when mass remains constant). So if we are falling freely we don't feel any force, as a result, force is equal to zero.
4) One finds that it is easier to open the door when a force is applied perpendicular to / far away from the hinges of the door. It becomes difficult to open the door if the force is applied closer or parallel to the hinges. It is because, in this situation, the torque is almost zero and as a result the door does not open. Also, for this reason, the handle of the door is placed at the end of the door opposite to the end where the hinges are attached.
I will surely help you how much I can.
Let's see the answers :
1) Hills have a sharpened top point with a very less area. Less the area, more the pressure and hence more will be the force exerted on the ball by the hill, and for this the ball bounce higher than on plains. A plain, being a flat surface, has a wide area (large area). More the area, less the pressure, and hence less the force for which it will exert less force on the surface of the ball and the ball will bounce comparatively less than hills.
3) Both the thief and load falls down with same acceleration due to gravity.As there is no relative motion between them, the load is considered to be in rest when compared to the thief. So, there is no possibility of force applied on the thief for zero relative acceleration between them.
Shortly, we can state it as Force is directly proportional to acceleration (when mass remains constant). So if we are falling freely we don't feel any force, as a result, force is equal to zero.
4) One finds that it is easier to open the door when a force is applied perpendicular to / far away from the hinges of the door. It becomes difficult to open the door if the force is applied closer or parallel to the hinges. It is because, in this situation, the torque is almost zero and as a result the door does not open. Also, for this reason, the handle of the door is placed at the end of the door opposite to the end where the hinges are attached.
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