General
✓✗A rectangular film of liquid is extended from (4 cm × 2 cm) to (5 cm × 4 cm). If the work done is 3 × 10−4 J, the value of the surface tension of the liquid is
- 8.0 N m−1
- 0.250 N m−1
- 0.125 N m−1
- 0.2 N m−1
General
✓✗A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be
- 1000
- 450
- 1800
- 225
General
✓✗An aeroplane gets dynamic lift mainly because
- air flows slower over the top of the wing
- air flows faster over the top of the wing, so the pressure there is lower
- the wing is lighter than air
- air is denser above the wing
General
✓✗On a temperature-time graph of a substance heated at a constant rate, the slope of the line for the liquid phase is smaller than for the solid phase. This shows that
- the specific heat of the liquid is larger
- the specific heat of the solid is larger
- the latent heat is zero
- the melting point is high
General
✓✗Water flows through a horizontal pipe. At a point where the area is 10 cm2 the speed is 1 m s−1 and the pressure is 2000 Pa above that at a second point. The speed at the second point is
- 1 m s−1
- 3 m s−1
- \( \sqrt5 \) m s−1
- 2 m s−1
General
✓✗The excess pressure inside a soap bubble of radius r and surface tension S is
- 8S/r
- 2S/r
- 4S/r
- S/r
General
✓✗A black body is at 727°C. It emits energy at a rate which is proportional to
- (1000)4
- (727)4
- (727)2
- (1000)2
General
✓✗The steel cables of cranes are made of many thin wires braided together rather than one solid wire mainly because
- it reduces the weight to zero
- braiding increases the density of steel
- thin wires have a larger Young's modulus
- this gives flexibility with the same strength
General
✓✗The hydraulic lift and hydraulic brakes work on
- Archimedes' principle
- Stokes' law
- Pascal's law
- Bernoulli's principle
General
✓✗Air (density 1.2 kg m−3) flows over the top of a wing of area 20 m2 at 70 m s−1 and under it at 60 m s−1. The lift on the wing is
- 7800 N
- 780 N
- 1560 N
- 15 600 N
General
✓✗A sphere, a cube and a thin circular plate, all of the same material, mass and surface finish, are heated to the same temperature and left to cool. Initially the fastest cooling is shown by
- all equally
- the sphere
- the cube
- the plate
General
✓✗A pendulum clock gains 10 s per day at 10°C and loses 10 s per day at 30°C. The temperature at which it keeps correct time and the coefficient of linear expansion of its rod are
- 25°C and about 4.6 × 10−5 K−1
- 20°C and about 1.2 × 10−5 K−1
- 20°C and about 2.3 × 10−5 K−1
- 15°C and about 2.3 × 10−5 K−1
General
✓✗A steel scale is correct at 0°C. A brass rod measured with it at 40°C reads 100 cm. If αsteel = 1.2 × 10−5 and αbrass = 1.8 × 10−5 K−1, the true length of the brass rod at 40°C is
- 99.952 cm
- 100.072 cm
- 100 cm
- 100.048 cm
General
✓✗A wire elongates by l when a load W is hung from it. If the wire goes over a smooth pulley and two weights W each are hung at its two ends, the elongation of the wire (full length the same) is
- l/2
- l
- 2l
- zero
General
✓✗A liquid drop of radius R breaks into 1000 identical small drops. The surface area increases by a factor of
- 1
- 1000
- 100
- 10