Important Questions

Questions you'll need to solve with Solutions

TOPIC: Conservation of Energy

Topic: heat & temperature

Q : When a sprinter bursts from the starting blocks, he/she generates considerable forward momentum. Is this an example where momentum is not conserved ?

Ans. Momentum is conserved. The blocks are grounded.......

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Q : A 5g object moving to the right with a speed of 20 cm/s makes an elastic head on collision with a 10g object initially at rest. Find : (a) the velocity of each object after collision & (b) the fraction of the initial energy transferred to the 10g object

Ans. For elastic collision, two equations hold :

Momentum conservation gives m1u1 + m2u2 = m1v1 + m2v2

and energy conservation yields u1 + v1 = u2 + v2 .........

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TOPIC: Forces & motion

Q : A penny is placed on an LP record that is slowly accelerating up to 78 rev/min. It is found that if the penny is placed at 0-080m or greater from the center , then the penny slides off the edge of the record. Find the co-efficient of static friction if the mass of the penny is 0.0032 kg

Ans. Here we're given the frequency of the LP and the mass of the penny. We know that; Frictional force = Co-efficient of friction * N

where N = Normal Reaction and Centripetal acceleration= v*v/r

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Q : A stuntman swings from

the end of a 4.10 m long rope along the arc of a vertical circle. If his mass is 72.5 kg, find the tension in the rope required to make him follow his circular path, assuming he starts rest when the rope is horizontal (a) At the beginning of his motion and (a) at the bottom of his arc

Ans. At the bottom of the arc, the tension must support the weight of the stuntman and the centripetal force , therefore Tension = mg + mv*v/r View full answer, Click

Q : A satellite of mass 615 kg is in circular orbit about the Earth at a height above the Earth equal to the Earth's mean radius. Find

(a) The satellite's orbital speed (b) The period of its revolution and

(c) The gravitational force acting on it

Ans. According to Newton's law of gravitation and second law of motion, when a body is in circular motion around another, a centripetal acceleration is caused. This acceleration is caused by gravity so that the force of gravity equals to.......... View full answer , Click

Q : A 6m ladder weighing 150 N rests against a smooth wall at an angle 55 degrees to the horizontal. A 550 N person climbs halfway up the ladder when it slips. What is the co-efficient of static friction between the ladder and the ground ?

Ans. Sum of forces along x-axis = 0 or F - R = 0 Where F = Friction force b/w ladder and the ground and........ View full answer , Click

Q : A laboratory thermometer reads 0.4 degrees Celsius at the ice point and 100.9 degrees Celsius at the steam point. What temperature will the thermometer read when the true temperature is 18.2 degrees Celsius ?

Ans. When true temperature is 0 degrees, thermometer reads 0.4 degrees and 100.9 degrees for.......... View full answer, Click

Q : A balloon is to be filled with helium ( density 0.178 kg/cubic meter ) while the air outside has density 1.29 kg/cubic meter. The mass of the empty balloon is 80 kg and it is to lift a load of 240 kg. What minimum volume is necessary for the lift off ? Assume that the balloon material and the load occupy negligible volume

Ans. The balloon will float when the weight of the displaced air is equal to the weight of the balloon with load

Also, Volume of the balloon = mass of..... View full answer, Click

Q : A block of material with a cross-sectional area of 15 cm square and length of 8 cm is at hand. A temperature difference of 30 degrees Celsius is established and maintained across the block. Find the rate of heat flow through it if

( a ) The material is Copper ( K = 397 J/s m C )

( b ) The material is air ( K = 0.0234 J/s m C ) and

( c ) The material is wood ( K = 0.08 J/s m C )

Ans. Rate of heat flow = K (thermal conductivity) *area/thickness*....... View full answer, Click

TOPIC : WAVES

Q : An 80 kg student sits down in his 920 kg car and his weight causes the car's springs to sink an additional 0.004 m. The student then gets out of his car and bounces it up down. Treating the system as a simple single spring and mass, calculate the frequency for the vertical vibration

Ans. A car is designed so that its vibrations attenuate very fast. When the boy sits in his car, the springs lower by an additional 0.004 m in the new equilibrium position, we cannot apply the conservation of........ View full answer, Click

Q : A student uses an audio oscillator of adjustable frequency to measure the depth of a water well. He reports two successive resonances at 52 & 60 Hz respectively. How deep is the well ?

Ans. We know that L =nv /4f where n=1,3,5,.... assumes a cylindrical well, Since the resonances are successive then......... View full answer, Click

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