# Tutor profile: Dhanalakshmi R.

## Questions

### Subject: Physics (Thermodynamics)

The carnot engine works between the temperatures 200 K and 350 K. Calculate the efficiency of engine and work done by the engine when the 300 J heat absorbed from the source.

Concept: The efficiency of carnot engine is e= 1- (T2/T1) Here T1 is the temperature of source and T2 is the temperature of sink. Solution: Given data Temperature of source is T1= 350 K. Temperature of sink is T2=200 K The efficiency of Carnot engine is e= 1- (T2/T1)= 1-(200 K/350 K) =0.428=0.43 The amount of work done by the engine is W= eQ= (0.428)(300 J) = 128.6 J

### Subject: Physics (Newtonian Mechanics)

A block of mass 10 kg is freely falling from the height 30 m and reaches the velocity 20 m/s just before reaching the ground. Find the amount of work done by the air drag.

Concept: Applying work energy theorem, Work done by all the forces = Change in kinetic energy Wmg+Wair= (1/2)mv^2 Here Wmg is the work done by the gravitational force. Wair is the work done by the air drag. Solution: Given data Mass of block is M= 10 kg Acceleration due to gravity is g= 9.80 m/s^2 Final velocity is v= 20 m/s Initial veloccity is v0=0 The work done by the air drag is Wair = (1/2)mv^2 - mgh =(1/2)(10 kg )(20 m/s)^2- (10 kg)(9.80 m/s^2)(30 m) =- 940 J

### Subject: Physics

An ball of mass M=4 kg moving with a initial velocity is 2i -4j m/s and collides with rigid wall and returns with a velocity is 2i+4 j m/s. Find the magnitude of impulse acting on the ball.

Concept: The impulse acting on the ball is equal to the change in momentum of the ball. The change in momentum of the ball is equal to subtract initial momentum from the final momentum. Solution: Given data Mass of the ball M = 4 kg Initial velocity is v0= 2i - 4j m/s Final velocity is v= 2i + 4j m/s The expression for the impulse acting on the ball is J= pf-pi = Mv- Mv0 =M(v-v0) =(4 kg)((2i +4j m/s) -(2i-4j m/s)) =(32 kg. m/s) j Hence, the magnitude of the impulse acting on the ball is |J| = 32 kg. m/s.

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