Question 8
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- Define upthrust.
- State one function of seat belts in automobiles.
- Give three examples of natural bodies that execute circular motion
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A stone of mass 300g is thrown vertically upward from the ground with a velocity of 10ms-1. Determine the:
- potential energy of the stone at maximum height;
- kinetic energy of the stone just before it reaches the ground, neglect air resistance. [Take g = 10ms-2]
- A stone is released from a height and it hits the floor later. State the energy transformations in the process.
Observation
Part (a) Well attempted by most candidates but poorly answered.
Part (b) Many candidates attempted this question but performed poorly. Most candidates
Part (c) Candidates performance was below average.
The expected answer is:
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Definition of upthrust
The upward force exerted by a fluid on an object immersed in it.
NOTE: Accept ‘liquid or gas’ for “fluid” -
Function of seatbelt
To secure the driver / passengers against harmful movement that may occur during sudden stoppage of the automobile. -
Examples of natural bodies that undergo circular motion
- Moon
- Earth
- Mars and any other planet
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Definition of upthrust
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Determination of potential energy at maximum height
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Determination of kinetic energy of stone just before it reaches the ground
At maximum height, P. E. = initial K. E. = 15 J
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Determination of potential energy at maximum height
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Energy Transformations in the process
P.E ----> K.E ---> P.E ---> Sound