The focal length of a lens is 30cm and the size of the image is a quarter of the object, then the object distance is

A car travelling at 30ms^-1decelerates uniformly to rest in a distance of 60m. If the driver has a mass of 80kg, which one of the following is the average retarding force in newtons necessary to retain him in his seat?

Refractive index of a material depends on

A body is acted on by forces X, Y, and Z that it in equilibrium. X is 5N, Y is 4N and zis 3N what is the angle between the direction of X and Z?

Under certain conditions, the rate of cooling of a given body is directly proportional to the difference between its temperature and that of its surroundings. The rate of cooling of the body is 12Kmin^-1when the temperature is 60⁰C. The surrounding temperature,in ⁰C, is

Optical fibres are based on the principle of

The capacitance of a parallel plate capacitor increases with the

A train is travelling at a a constant speed of 25ms^-1 along a straight level track. As it a point P,a constant braking force is applied and the train comes to rest at a distance 500m from P. On another occasion, the same train travelling at 50ms^-1 is subject to the same constant braking force applied at the same point. All other forces may be neglected. On this occasion, the train comes to rest at a distance in m from P of

A constant volume gas thermometer indicates a pressure of 20kpa when in thermal equilibrium at 273K. When in thermal equilibrium with a steam bath at a temperature of 100⁰C the thermometer will indicate a pressure, in kpa, of approximately

Two identical spheres are joined in parallel, charged to a potential V and then separated and then connected in series

A parallel plate capacitor is made with air as medium between the plates has a capacitance of 10microfarads. The area of the capacitor is divided into two equal halves and filled with two media having dielectric constants K₁=1 and k₂= 4. The capacitance of the system will now be

A block of ice, mass 1.5kg, absorbs thermal energy from its surroundings at a steady rate of 50W. The specific latent heat of fusion is 3.0 x 10⁵Jkg^-1. The time in hours ,for the ice to melt is

A body of mass 4kg falls vertically through air. When the magnitude of the air resistance is 30N, what is the acceleration of the body?

A crane has a maximum safe working load of 1200kg and is used to lift a concrete block of mass 1000kg. What is maximum safe upwards acceleration of the block whilst being lifted?

A lunar landing module is descending to the moon's surface at a steady velocity of 10ms^-1. At a height of 120m, a small object falls from its landing gear. Taking the moon's gravitational acceleration as 1.6ms^-2, at what speed in ms^-1 does the object strike the moon?

Which one of the following is the correct unit for specific latent heat of fusion?

A parallel plate is capacitor is made by stacking n equally spaced parallel plates connected alternatively. if the capacitor between any two plates is C, then the resultant capacitance of the system will now be

A dielectric slab of dielectric constant 5 is covered from all sides with a metallic foil. The system is introduced into the space of a parallel plate capacitor of capacitance 10microfarad. The slab fills almost the almost the entire space between the plates but does not touch. The capacitance will become nearly

A sky -diver has a mass of 80kg. The sky -diver attains a vertical speed 30ms^-1, shortly after stepping from an aircraft. During this period the sky -diver falls 100m.What is the mean force of air resistance experienced by the sky -diver during this part of the fall?

A number of capacitors each of capacitor 1 microfarad and each one of which gets punctured if the potential difference just exceeds 500V is applied, are provided. The an arrangement suitable for giving a capacitance of 2microfarads across which 3000V may be applied, requires atleast

A hollow metal sphere of radius 10cm is charged such that the potential on its surface is 80V. The potential at the centre of the sphere.

At sunrise or sun set the sun looks more red than at mid - day, because

For an astronault in space, the sky appears

An achromatic doublet is formed by joining

A body of mass 4kg is is accelerated from rest from rest by a steady force of 9N. What is its speed when it has travelled a distance of 8m?

Which thermodynamic temperature is equivalent to 501.85⁰C?

A car travelling at 30ms^-1 decelerates uniformly to rest in a distance of 60m. If the driver has a mass of 80kg, which one of the following is the average retarding force, in newtons , necessary to retain him in his seat?

A force of 3800N is required to move a vehicle of mass 1500kg at a constant speed along a horizontal road. In travelling 300m along the road, the work in KJ, done against frictional forces is

There are two +1microcoulombs and 5microcoulombs. The ratio of the forces acting on them will be

The twinkling of stars is due to