Question

1. A wheel rotates at an angular velocity of 30rad/s. If an acceleration of 26rad/s^2 is applied to it, what will its angular velocity be after 5.0s?

A. -160 rad/s    B. 30 rad/s   C. 56 rad/s    D.160 rad/s

2. A heat engine with 50.0% efficiency consumes 70.0kJ of energy by heat. What is the waste heat it produces?

A. -70.0 kJ    B. -35.0 kJ    C. 35.0 kJ   D. 70.0kJ

3. Why are the Sun and Earth not in thermal equilibrium?

A. The mass of the Sun is much greater than the mass of Earth.

B. There is a vast amount of empty space between the Sun and Earth.

C. The diameter of the Sun is much greater than the diameter of Earth.

D. The temperature of the Sun is much higher than the temperature of Earth.

4. A heat engine takes in 8.5kJ of energy by heat and does 3.8kJ of work. What is its efficiency?

A. 55%    B. 5.50%     C. 4.50%   D. 45%

5. What is thermal efficiency of an engine? Can it ever be 100%? Why or why not?

A. Thermal efficiency is the ratio of the output (work) to the input (heat). It is always 100%.

B. Thermal efficiency is the ratio of the output (heat) to the input (work). It is always 100%.

C. Thermal efficiency is the ratio of the output (heat) to the input (work). It is never 100%.

D. Thermal efficiency is the ratio of the output (work) to the input (heat). It is never 100%.

Answer 1

1)i=30 rad/s  =26 rad/s^2 using  f =i+ t t=5sec   f=30+(26*5)=30+130=160 rad/sec. option D

2) 50% is only converted into work rest 50% is waste heat so 0.5 *70kJ =35KJ OPTION c.

3) OPTION d) thermal equilibrium means there should be no transfer of energy and they should be isolated but thats not the case heat is transferred from sun to earth because of temperature difference

4)the efficiency of a heat engine measured by the ratio of the work done by it to the heat supplied to it. so efficiency =(3.8/8.5)*100=0.4475*100 =45% rounding off so option D

5)option D as 100% conversion of heat nto work is not possible there will some dissipations