SPM Physics Pressure Q12
12. Diagram 6 shows an empty glass is at rest on a table.
Rajah 6 menunjukkan satu gelas kosong berada dalam keadaan rehat di atas meja
How does the pressure exerted by the glass on the table change as the water is gradually poured into it?
Bagaimanakah tekanan yang dikenakan oleh gelas pada meja berubah apabila air dituang ke dalamnya secara perlahan-lahan?
SPM Physics Pressure Q12 Solution
Pressure = Force/Area
P = F/A = mg/A = (ρV+m_glass)*g/A , where V is the volume of water added and m_glass is the mass of the empty glass.
In other words, P = ρVg/A + C, where the C constant is equal to m_glass*g/A.
As you can see, since the density of water, ρ and gravitational acceleration, g is constant, P should be linearly proportional to V. However, when V = 0, the pressure is not equal to zero but has a fixed value, therefore it should not pass through the origin. (hence it is not “directly” proportional)
So the answer should be B, where pressure varies linearly with volume of water added, and intersects the y-axis at a certain positive value when V = 0.