Question

a car traveling 50km/h east accelerates at 0.25 m/s² west. What will be its velocity and displacement:

a) at 3min?

b) when it passes it's the initial position?

Answer 1

a) initial velocity is 50 km/h = 13.89 m/s(positive means east)

a = -0.25 m/s^2(negative means towards west)

The displacement when t = 3 min = 180 s is

$d=u t +\frac{1}{2}a t^2=13.89\times 180-0.25 \times 180^2/2=-1550.\,m=-1.55 km$

displacement is negative because it is in the west. The magnitude of displacement is d = 1.55 km = 1550 m

velocity after t = 180 s is

$v=u+a t = 13.89-0.25\times 180=-31.11\,\,m/s$

In km/h the answer is v = - 112 km/h

velocity is negative because it is in the west direction.

b) When it passes initial position d = 0 m 0 km

Therefore

$v^2 = u^2$

$v = - u = - 13.89\,m/s= - 50\, km/h$

velocity is negative because it is in the west direction.