I am having difficulty trying to choose which equation of kinematics to use on these 3 questions.
Could you please guide me in the right direction
Thank you very much
Constant acceleration means that the average speed may be calculated in a simple way from the initial speed and the final speed. It is just the arithmetic average (vi+vf)/2. Another expression for average speed is the distance covered divided by the time it took. Average speed is average speed no matter how it is calculated so (vi+vf)/2=60/6=10m/s. But we are given the fact that vf=15m/s so vi must be 5m/s to make (vi+vf)/2=10.
The acceleration, being constant, is simply calculated by the change in speed divided by the time it took, or (15-5)/2m/s/s = 5m/s/s.
With constant acceleration of 5 m/s/s it will take 1 second to reach the initial speed and therefore the initial point. The average speed between rest and the initial point is (0+5)/2m/s = 2.5m/s. At an average speed of 2.5m/s, in 1 second the distance covered is 2.5 meters.
Again, if my arithmetic is correct, we have arrived at the solution without plugging any of the kinematics equations directly. Understanding is a much more powerful tool than is knowledge. It allows you to answer questions that have never been previously asked. People pay good money to anyone with that ability.