Answer:
0.237 (23.7 %)
Explanation:
The thermal efficiency of an engine is given by:
where
W is the useful work output of the engine
is the heat in input
Here we have:
and the work done is the total heat in input minus the heat exhausted:
So, the efficiency is
(23.7 %)
a) 52.5 m
b) 16.0 m/s
Explanation:
a)
The motion of a car slowed down by friction is a uniformly accelerated motion, so we can use the following suvat equation:
where
v = 0 is the final velocity (the car comes to a stop)
u = 28.7 m/s is the initial velocity of the car
a is the acceleration
s is the stopping distance
For a car acted upon the force of friction, the acceleration is given by the ratio between the force of friction and the mass of the car, so:
where:
is the coefficient of friction
is the acceleration due to gravity
Substituting and solving for s, we find:
b)
In this case, the car is moving on a wet road. Therefore, the coefficient of kinetic friction is
Here we want the stopping distance of the car to remain the same as part a), so
We can use again the same suvat equation:
And since the final velocity is zero
u = 0
We can find the initial velocity of the car: