Physics Answers

Find the change in entropy when (a) 3.0 kg of boiling water changes to steam at 100ºC, (b) 3.0 kg of water is heated from 20ºC to 80ºC, and (c) 2.0 kg of water at 30ºC are mixed with 5.0 kg of water at 75ºC and the mixture allowed to reach equilibrium.

A perfect heat engine takes in heat at 237ºC and rejects heat at 97ºC. What is the efficiency of the engine? How much heat is rejected for every 1000 joules of work done?

If the temperature of a hot reservoir is 400K, what must the exhaust temperature be so that the efficiency of an ideal heat engine is 25%?

If all the energy of a 20-g bullet travelling at 1km/s is converted into heat, how many calories are generated?

A ray of light passing from water to air is deviated 10° from its original direction.What is the a) angle of incidence b) angle of reflection and

c) angle of refraction?

A ray of light passing grom water to air is deviated 10° from its original direction.what is the a) angle o incidence b) angle of reflection c) angle of refraction?

A body of mass 3M at rest explodes into two pieces of mass M and 2M. What is the ratio of the kinetic energy of M to that of 2M? (Ans:2)

A person of mass m stands on weighing scales in an elevator. The elevator is accelerating upwards with acceleration a. The reaction force from the scales on the person is R. What is the reading on the scales? (Ans: R)

Two smooth reflecting surfaces (A and B ) ate perpendicular to each other.Light strikes surface A at a point 12cm from the point of intersection of surfaces A and B.If the angle of incidence is 30 degrees, how far from the point of intersection of the two surfaces will yhe reflected light from surface A steike surface B?

A body that started from rest moves with constant acceleration in a straight line. After travelling a distance d the speed of the car is v. What is the distance travelled when the speed of the car was v/2? (Ans: d/4)