Question
(a) A metal ruler with a rectangular cross-section is heated in an oven.
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State two things that happen to the atoms of the metal.
1. ……………………………………………………………………………………………………………….
2. ……………………………………………………………………………………………………………….[2]
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State what happens to
1. the length of the ruler, ………………………………………………………………………………
2. the width of the ruler, ………………………………………………………………………………..
3. the thickness of the ruler. ………………………………………………………………………….. [2]
(b) The nut in Fig. 5.1 has become jammed on the bolt, so that it will not rotate.
Explain why heating the nut with a very hot flame is likely to free the jammed nut.
…………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………….. [2] [Total: 6]
Answer/Explanation
Ans: (a) (i) move/vibrate/oscillate faster OR increase/gain KE move (further) apart OR (they) separate
(ii) any 1 increases/enlarges/gets bigger/expands o.w.t.t.e. all three increase
(b) nut/hole expands/enlarges ignore particles expand/enlarge bolt doesn’t expand (as much)
Question
(a) Explain, in terms of molecules, why liquids are very difficult to compress.
(b) Fig. 3.1 shows a device that uses liquid pressure to lift heavy boxes.
The boxes are lifted by pumping oil into the cylinder.
The force upwards on the piston due to the oil, and the force downwards on the piston due to the air above the piston, combine to produce a constant force of 8800 N.
The pressure of the air is 1.0 × \(10^5\) Pa and the cross-sectional area of the bottom surface of the piston is 0.016 \(m^2\).
(i) Calculate the pressure of the oil at the bottom surface of the piston.
pressure =………………………………………………
(ii) As the boxes are lifted, the depth of the oil increases.
Explain why the pump must exert an increasing pressure on the oil as the depth of the oil increases.
(iii) Suggest one reason why the force of 8800 N in (b) cannot lift boxes of weight 8800 N.
Answer/Explanation
Answer:
(a) molecules (already very) close / touching
(repulsive) forces (very) large
(b)(i) \( 6.5 \times 10^5\) Pa
(p =) F / A in any form or 8800 / 0.016 or ( \(F_{air}\) =)1.0 × \(10^5\) × 0.016
\(5.5 × 10^5 \) or 5.5 × \(10^5\) (+ 1.0 × \(10^5\)) or (1600 + 8800) / 0.016\)
(b)(ii) pressure due to (increased height of) oil in cylinder mentioned or pressure (in liquid) increases as depth increases
to keep the upwards force constant or to lift the (extra) oil
or to counteract / oppose the increased pressure / force / weight of the oil
(b)(iii) (initial) force has to be greater than 8800 N to start the motion
or the upwards force (just) balances the weight (so no movement) or piston / oil has weight or friction (between moving parts)