Question

A body starting from rest accelerates uniformly at the rate 10cm/s^2 and retards uniformly at the rate of 20cm/s^2.Find the least time in which it can complete a journey of 5km if the max velocity attained by the body is 72km/hr.

Answer 1

Answer:hi hope this helps

Explanation:

Answer 2

Answer:

Least time is 5 min to complete a journey of 5 km.

Explanation:

Given,

acceleration(a) = 10 $cm/s^2$ ,initial velocity (u) = 0 ,Final velocity(v) = 2000 $cm/s$

Now we know that,

                                  $v = u +at_1$

                            → 2000 = 0 + 10 x $t_{1}$

                           →  $t_1 = \frac{2000}{10} =200 \ sec$

Distance travelled in 2 sec ,

                 $S = ut_1 +\frac{1}{2} a t_{1}^{2}$

                       = 0 + $\frac{1}{2} * 10 *(200)^2$

                       = $\frac{400000}{2}$ = 200000 cm =2000 m =2 km

Again,retarded acceleration(a) = -20 $cm/s^2$ , initial velocity(u) = 2000cm/s

and final velocity(v) =0

                               0 = 2000 - 20 x $t_{2}$       [Using,v =u +at]

                             →  $t_{2}$ = $\frac{2000}{20}$ = 100 sec

∴ Total time,t = $t_1 + t_2$ = (200+100)sec = 300 sec = 5 min