Question

A motorist is travelling at 54km /hr when he observes a traffic signal at a distance of 280m ahead turning red at time t = 0. If he decides to decelerate & then accelerate by the same magnitude, so as to pass the signal at 54km/hr at t = 28 seconds, when the signal turns green, then: (A) Magnitude of deceleration is 5/7 $m/s^2$ (B) Magnitude of deceleration is 1$m/s^2$ (C) Minimum speed reached is 5m/s (D) Minimum speed reached is 10m/s

Answer 1

Explanation:

Given A motorist is travelling at 54 km /hr when he observes a traffic signal at a distance of 280 m ahead turning red at time t = 0. If he decides to decelerate & then accelerate by the same magnitude, so as to pass the signal at 54 km/hr at t = 28 seconds, when the signal turns green, then: (A) Magnitude of deceleration is 5/7   (B) Magnitude of deceleration is 1  (C) Minimum speed reached is 5m/s (D) Minimum speed reached is 10 m/s

• We have A B and C direction. The motorist travels a distance of A to B 140 m and B to C 140 m in 14 secs and from B to C in 14 secs.
• So initial velocity u = 54 km/hr  
•                                  = 54 x 1000 / 3600
•                         Or u = 15 m/s
• Now the distance from A to B obtained from equations of motion,
•                              S = ut + ½ at^2
•                           140 = 15 x 14 – ½ x a x (14)^2
•                           140 = 210 – 98 a
•                        So 98 a = 70
•                        Or a = 70 / 98
•                          Or a = 5/7 m / s^2
• Now we have V = u – at
•                            = 15 – 5/7 x 14
•                    = 15 – 10
•         Or V = 10 m/s
•     Minimum speed reached is 10m/s

Reference link will be

https://brainly.in/question/2314258

Answer 2

Answer:

V=10m/s will be the answer