Question

a block of mass 8kg is moving with a velocity of 36km/hr.If it's velocity is reduced to 18km/hr in 0.5 sec.What is the retarding force on the block.
a) 20N. b) 40N c) 60 N
d)80N

Answer 1

We will use the below formula,

$v \: = vo \: + at$

where,
v = final velocity = 18 km/hr = 5 m/s
vo = Initial velocity = 36 km/hr = 10 m/s
a = acceleration
t = time difference = 0.5 s

Now substituting all values in the above equation,

5 = 10 + a(0.5)

-5/0.5 = a

a = -10 m/s^2

Now finding the force,

F = ma
F = (8)(-10)
F = -80 N

Negative sign shows that the direction of the force is opposite to the direction of the object.