An object moving at 36 km/h reduces its speed to 18 km/h in 2sec. If the mass of the object is 20 kg, find the average force acting on the object.

-50 N

Explanation:

Givens:

V_i = 36 km/h

V_f = 18 km/h

t = 2 s

m = 20 kg

First we have to convert our km/h into m/s:

(36 km*(1000 m/1 km)) / (60 min *(60 s/1 min)) = 10 m/s

(18 km*(1000 m/1 km)) / (60 min *(60 s/1 min)) = 5 m/s

a = (V_f - V_i)/t

a = (5 m/s - 10 m/s) / 2 s

a = -2.5 m/s^2

F = m(a)

F = 20 kg(-2.5 m/s^2)

F = -50 N

It's a negative force meaning its acting on it opposite its current direction of movement.

increases it