Question

A body moving at a speed of 15 m/s. Attended a speed of 180 km/hr in 7 seconds. Calculate the retardation it gained.​

Answer 1

initial speed of body, u = 15m/s

final speed of body, v = 180 km/h

= 180 × (1000m)/(3600sec)

= 180 × 5/18 m/s

= 50 m/s

and time taken , t = 7 sec

here speed increases with time, so body moves with acceleration not retardation.

To find acceleration, using formula,

v = u + at

or, 50 = 15 + a7

or, 35 = 7a

or, a = 5m/s²

hence, acceleration is 5m/s²

Answer 2

Initial speed of the body(u) = 15 m/s.

Final speed of the body(v) = 180 km/hr. = 180 × 5/18 m/s. =  50 m/s.

Change in Velocity = v - u = 50 - 15 = 35 m/s.

Time taken to gin the speed(t) = 7 seconds.

Using the Galileo's first equation of motion,

 v - u = at

 35 = a × 7

a = 5 m/s².

Since, acceleration is positive, which means that the body is accelerated to increase the speed and thus, it is not retarded.

Hope it helps.