Motion

Question

A sports car accelerates along a straight line from rest at a rate of 6 ms^ -2 for 4s and then its acceleration changes to -4ms^ -2 for 2s.
(a)Find the maximum speed of the car. Express the answer in km h^-1.
(b)Find the final speed of the car. Express the answer in km h^-1.
(c)Find the average acceleration of the car.Express the answer in ms^-2.

answer:
(a)86.4km h^-1
(b)57.6km h^-1
(c)2.67ms^-1

Answer 1

(a)Find the maximum speed of the car. Express the answer in km h^-1.

v = u + at = 0 + 6X4 = 24 m/s = 24X3600 = 86400 m / hr = 86.4 km / h

(b)Find the final speed of the car. Express the answer in km h^-1.

v = u + at = 24 + (-4)(2) = 16 m/s = 16X3600 = 57600 m/h = 57.6 km/h

(c)Find the average acceleration of the car.Express the answer in ms^-2.

Actually, I don't know what is "average acceleration" . I do it like this.

( 6X4 + (-4)X2 ) / ( 4 + 2 ) = 2.667 ms^-2