Question

Pls guys answer my question...

the third part of the question is
iii) the speed of car after 2 s of applying the brakes

do NOT give wrong answers or else I'll report your answer ​

Answer 1

i) The speed of car in m s⁻¹

To convert speed from km h⁻¹ to m s⁻¹, we multiply with 5/18

Given speed in km h⁻¹ = 18 km h⁻¹

So, speed in m s⁻¹ = 18 × 5/18 = 5 m s⁻¹

Answer : 5 m s⁻¹

ii) The retardation

We have, u (initial velocity) = 5 m s⁻¹

v (final velocity) = 0 m s⁻¹ (since it comes to rest)

and t = 5 s

We know that acceleration = (v - u)/t

⇒ (0 - 5)/5 = -5/5 = - 1 m s⁻²

Retardation is negative acceleration, so we say there is a retardation of 1 m s⁻²

iii) The speed of car two seconds of applying the brakes.

Let the speed of car after 2 seconds of applying the brakes be v

We have,

u = 5 m s⁻¹

a = - 1 m s⁻²

t = 2 s

We know that

a = (v - u)/t

⇒ - 1 = (v - 5)/2

⇒ -2 = v - 5

⇒ v = 3 m s⁻¹

Answer 2

Answer:

a). u = 5 m / sec

b). a = - 1 m / sec²

c).  v = 3 m / sec

Explanation:

We have :

Speed of car = 18 km / hr

a.

Speed of car in term of m / sec = 18 × 5 / 18 = 5 m / sec

b.

We have :

Initial velocity u = 5 m / sec

Final velocity v = 0 m / sec

Time t = 5 sec

Using first equation of motion :

v = u + a t

Putting values here we get :

0 = 5 + 5 a

5 a = - 5

a = - 1 m / sec²

Here negative sign represent retardation or acceleration in opposite direction.

c).

In these case we have :

Initial velocity u = 5 m / sec

Acceleration a = - 1 m / sec²

Time t = 2 sec

We are asked to find final velocity :

Again using first equation :

v = u + a t

= > v = 5 + ( - 1 × 2 ) m / sec

= > v = 5 - 2 m / sec

= > v = 3 m / sec

Hence we get all required answer.