Question

24. A car travelling with a velocity of 80 km/h slowed down to 44 km/h in 15 s. The retardation is
(1) 0.67 m/s2
(3) 1.25 m/s2
(2) 1 m/s2
(4) 1.5 m/s2
​

Answer 1

ANSWER:

Retardation = 0.67 m/s²

__________________

Explanation:

given that,

A car travelling with a velocity of 80 km/h slowed down to 44 km/h in 15 s.

here,

initial velocity of car = 80 km/h

by changing of initial velocity km/h into m/s

80 km/h

= 80000m/60 × 60s

= 22.222 m/s

final velocity of car = 44 km/h

by changing of final velocity km/h into m/s

44 km/h = 44 × 1000m/60 × 60s

= 12.222 m/s

given time for retardation = 15 seconds

now,

we have,

initial velocity(u) = 22.222 m/s

final velocity(v) = 12.222 m/s

time(t) = 15 s

now ,

by the equation of motion

v = u + at

where,

a = acceleration of the car

putting the values,

12.222 = 22.222 + a(15)

15a + 22.222 = 12.222

15a = 12.222 - 22.222

15a = -10

a = -10/15

a = -2/3

a = -0.666 m/s²

a = -0.67m/s²

negative acceleration shows the retardation ,

so,

Retardation = 0.67 m/s²

___________________

so,

correct option

(1) 0.67 m/s²

Answer 2

☞ A car traveling with a velocity of 80 km/hr

Car is in motion means it's initial velocity (from starting) is 80 km/hr.

• u = 80 km/hr.

=> $\dfrac{80\:\times\:1000}{3600}$

=> 22.22 m/s.

_______________________________

☞ The car slowed down to 44 km/hr

Means the final velocity of the car is 44 km/hr in 15 sec.

• v = 44 km/hr.

=> $\dfrac{44\:\times\:1000}{3600}$

=> 12.22 m/s

• t (time) = 15 sec

______________________________

☞ We have to find the retardation means (a).

» From first law of Equation.

$\boxed{v\: =\: u\: +\: at}$

We know the values of v, u, and t.

Put them in above equation.

=> 12.22 = 22.22 + a (15)

=> 12.22 - 22.22 = 15a

=> - 10.00 = 15a

=> a = $\dfrac{-10.00}{15}$

=> a = - 0.6667

=> a = - 0.67 m/s² (approx.)

_______________________________

The retardation is 0.67 m/s²

Option (1)

______________ [ANSWER]