Mechanics | Relativity Answers

A powerful motorcycle can produce an acceleration of 3.00 m/s2 while traveling at 90.0 km/h. At that speed, the forces resisting motion, including friction and air resistance, total 450 N. What force does the motorcycle exert backward on the ground to produce its acceleration if its mass with rider is 240 kg?

A particle moves along a straight line following the law
V= u+√(2as) then its acceleration
a. Increase with time
b. Decrease with time
c. Constant
d. N.O.T.

Hello,

This question relates to finding a constant acceleration using average velocity. In the acceleration questions posted at the beginning of the Khan Academy's MCAT Prep Acceleration section, there is one that asks for the constant acceleration to be solved for when a dragster travels 400 m in 4 seconds. The correct answer is displayed as 50 m/s/s, and the hints suggest solving with the d = 1/2at^2 formula.

Here is what I don't get: when I use the d = 1/2at^2 formula to solve for acceleration, I get the correct answer (50m/s/s). However, when I try to use the average velocity formula, a = 1/2(vi+vf) / t ---- I don't get the correct answer (12.5 m/s/s).

Could someone explain this for me, please? I would love to understand why I can't use acceleration = average velocity/time to solve this problem correctly, or what I have done wrong in trying to do so.

Thanks!!

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