Question

A car traveling with a velocity of 80 km/h slowed down to 44 km/h in 15s. The retardation is
A) 0.67m/sec.sq.
B) 1m/sec.sq.
C) 1.25m/sec.sq.
D) 1.5m/sec.sq.​

Answer 1

$\huge \boxed { \sf \color{silver}{a) \: 0.67 \: mp {s}^{2} }}$

Explanation:

Given -

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

.

Solution -

First we will convert the velocity in m/s.

To change km/h to m/s, multiply velocity to 5/18

$\sf80 \: kmps = \frac{80 \times 5}{18} mps \\ = \sf22.22 \: \: mps \\ \\ \sf44 \: kmps = \frac{44 \times 5}{18} mps \\ \sf= 12.22 \: mps$

Now,

initial velocity (u) = 22.22 m/s

Final velocity (v) = 12.22 m/s

Time taken (t) = 15 sec

.

Acceleration (a), we will find acceleration then change into retardation.

.

$\sf \: a = \frac{v - u}{t} \\ \\ = > \sf \frac{12.22 - 22.22}{15} mp {s}^{2} \\ \\ \sf = > \frac{ - 10}{15} mp {s}^{2} \\ \\ \sf= > - 0.66..mp {s}^{2} (approx \: - 0.67 {mps)}^{2}$

Hence acceleration = -0.67 m/s²

Retardation in negative acceleration, so -0.67 m/s² acceleration = 0.67 m/s² retardation.

.

So retardation = 0.67 m/s²

hope it helps.