Question

The speed of a goods truck falls from 18 km/h to 9 km/h in moving a distance of 75 m. If the retardation is constant how much further will the truck travel before coming to rest

Answer 1

$\longmapsto$ Initial velocity(u) = 18 km/h

$\longmapsto$ Final velocity(v) = 9 km/h

$\longmapsto$ Distance(s) = 75 m

We know,

v² = u² + 2as

⇒(9)² = (18)² + 2 × a × 75

⇒81 = 324 + 150a

⇒ -243 = 150a

⇒a = -243/150

⇒a = -1.62 m/s²

Now,

distance travelled by the goods truck before coming to rest = S

Initial velocity(U) = 9 km/h

Final velocity(V) = 0 m/s

Acceleration(a) = -1.62 m/s²

Again,

V² = U² + 2aS

⇒(0)² = (9)² + 2 × -1.62 × S

⇒0 = 81 - 3.24S

⇒ -81 = -3.24S

⇒S = -81/-3.24

⇒S = 25 km

∴ So, the truck will travel 25 km before coming to rest if the retardation is constant.