Answer: 15m/s
Explanation: <u>Average</u> <u>Velocity</u> is vector describing the total displacement of an object and the time taken to change its position. It is represented as:

At t₁ = 1.0s, displacement x₁ is:

x(1) = 28
At t₂ = 4.0s:

x(4) = 73
Then, average speed is

v = 15
The average velocity of a car between t₁ = 1s and t₂ = 4s is 15m/s
C: the mechanical energy isn't conserved. Some energy was lost to friction.
Answer:
Before start of slide velocity will be 14.81 m/sec
Explanation:
We have given coefficient of static friction 
Angle of inclination is equal to 


Radius is given r = 28 m
Acceleration due to gravity 
We know that 



So before start of slide velocity will be 14.81 m/sec