An engine takes 3,000 J from a hot reservoir and expels 2,400 J to a cold reservoir. What is the thermal efficiency of the engine? 20% 45% 60% 80%

The thermal efficiency of the engine is 80%

The parameters given in the question are;

Input= 3000J

Output= 2,400J

Output/Input × 100

= 2400/3000 × 100

= 0.8 × 100

= 80%

The thermal efficiency of the engine is 80%

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80%

Explanation:

Thermal efficiency is a measure of the extent to which a heat engine is able to convert to other form. It is measure in percentage.

Thermal efficiency = × 100%

Where is the input energy and is the output energy.

Given that: = 2400 J and   = 3000 J, therefore:

Thermal efficiency = × 100%

                               = 80%

The thermal efficiency of the engine is 80%.

massxgravity x heght=weightxheight= pe

4900=490xh

h=10

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s