A motorcyclist started a race from START line and from rest, and accelerated with the acceleration of 2 m/s2 for 7 seconds. Then he increased the acceleration to 4 m/s2 and went with that acceleration for 8 seconds. What was the racer’s position from the START line after 7+8 seconds from the start of the race?

289 m .

Explanation:

s = ut + 1/2 at² , u is initial velocity , t is time , a is acceleration and s is distance covered .

For t = 7 s

s = 0 + 1/2 x  2 x 7²

= 49 m

velocity after 7 s

= a x t = 2 x 7 = 14 m /s

for next 8 s , initial velocity u = 14 m /s

S = ut + 1/2 at²

= 14 x 8 + 1/2 x 4 x 8²

= 112 + 128

= 240 m

Total displacement in 7 + 8 s

= 49 + 240 = 289 m .

the working equation for the angular size is the product of the physical size and 360 degrees divided by the product of two pi and distance from earth. the minimum size would be 0.559 degrees while the maximum size would be 0.49 degrees. 

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.