# An iron sphere of mass 1 kg is moving with a velocity of 20m/sec on a cemented floor. It comes to rest after travelling a distance of 50m. Find the force of friction between the sphere and the floor.

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by Deleted account
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2015-07-23T22:09:47+05:30
Let initial velocity be u
final velocity be v
acceleration be a
mass= 1000g.
distance= 50m
acc. to formula v2=u2-2a*s
so,   0 = 400- 2*a*50
-400= -100*a
a = 4 m/s2
F = MASS * ACCELERATION
F =  1000*4
= 4000N.
Does u2 mean u square
You actually need to convert 1000g to 1kg, and then calculate, so ans is wrong
but thanks for atleast attempting
2015-07-23T22:15:42+05:30
Mass of sphere, m = 1kg
initial velocity, u = 20 m/s
final velocity, v = 0
distance travelled, s = 50m
let the friction acting = f

Here, the kinetic energy of the ball is being dissipated to overcome friction. So, according to conservation of energy,

the change in kinetic energy = work done by friction

So friction acting is 4N. The negative sign denotes that it acts in the direction opposite to the motion of the sphere.

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using equations of motion,
let the acceleration due to friction = a
v² - u² = 2as
⇒ 0 - 20² = 2×a×50
⇒ -400 = 100a
⇒ a = -400/100
⇒ a = -4 m/s²

mass of sphere = 1 kg
friction = ma = 1×4 = 4N
you are welcome!!
you can also do by using equations of motion.
I used energy conservation method.
Yeah actually I wanted equations of motion
You can just say which one applies here
We still didn't go to the topic of energy