True because friction happens when two things are rubbed against each other and it creates force and sliding something vigorously against something else can create force.
Answer A sounds about right
It means that they were set earlier therefor they are older.
Answer:
Part a)

Part b)

Explanation:
Diameter of the circle = 24 ft
Diameter = 731.52 cm = 7.3152 m
now the horse complete 144 trips in one hour
so time to complete one trip is given as


now the speed of the horse is given as



Part a)
Now we know that the power is defined as rate of work done
it is given as




Part b)
Work done to climb up to 3 m height is given by

now we have




now we know that 1 HP = 746 Watt
so we have

From the given information, we don't know. All we can tell is the net effect of all the changes during those 4 seconds ... the "averages".
The average change in speed is an increase of 72 km/hr (20 m/s) during that time.
The average acceleration is a constant 18 km/hr/sec (5 m/s^2) during the same time.
But both the speed and the acceleration may have gone up or down many times during the 4 seconds.