A car starts from rest and accelerates uniformly for 5s until it attains a velocity of 30m/s. It then travels with uniform velocity for 15s before decelerating uniformly to rest in 10s

Physics Jamb, Waec, Neco Past Questions & Answers on Speed, Velocity and Acceleration

QUESTIONS 67. A car starts from rest and accelerates uniformly for 5s until it attains a velocity of 30m/s. It then travels with uniform velocity for 15s before decelerating uniformly to rest in 10s. 

(i) Sketch a graph of the motion. 

(ii) Using the graph above, calculate the 

I. acceleration during the first 5s, 

II. deceleration during the last 10s, 

III. total distance covered throughout the motion. 

NECO 2009E11 

Ans: 

I. 6ms–² 

II. 3ms'² 

III. 675m

SOLUTIONS 

Find acceleration for the first 5sec:

a =(v-u)/t

v=30m/s , u =0m/s , t=5sec

a = (30-0)/5 = 6m/s-².

I) 

II. decceleration in the last 10 sec:

a = (v-u)/t

t=10sec , v =0m/s (because at decceleration initial velocity becomes final velocity), u= 30m/s

a = (0-30)/10 , 

a= -3m/s–².

III. Total distance :

using formula of the graph of shape . Area of a triapezium

A =1/2(a+b) x h.

h = 30 , a = 15( the second time).

b = 30 (total time)

A = 1/2(15+30) x 30 

A = 45 x 15

A = 675km.