Acar moved 60 km east and 90 km west. what is the displacement? me 

assume the east-west direction along the x-axis such that east lies in positive x-direction and west lie in negative Y-direction.

In unit-vector notation , individual displacement can be represented as

A = displacement of car in east direction = 60 i

B = displacement of car in west direction = - 90 i

D = total displacement of the car

Total displacement of the car is given as

D = A + B

inserting the values

D = 60 i + (- 90 i)

D = - 30 i

negative sign indicates the direction in west

hence net displacement is 30 km in west direction

b.a device that inputs heat into a cool object