Question

How much force is exerted on a 13kg object accelerating from 20m/s to 12m/s in 3.5s?
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Answer 1

Given :

Mass of the object, m = 13 kg

Initial velocity, u = 20 m/s

Final velocity, v = 12 m/s

Time taken, t = 3.5 s

To find :

Force exerted by the object

Solution :

first of all we have to find accerlation as we are provided with initial Velocity, final velocity and time we can use first equation of motion .i.e.,

➠ v = u + at

here ,

• v denotes final velocity
• u denotes initial velocity
• a denotes acceleration
• t denotes time taken

by substituting all the given values in the equation,

➠ 12 = 20 + (a)(3.5)

➠ 12 - 20 = 3.5a

➠ -8 = 3.5a

➠ a = -8 /3.5

➠ a = - 2.28 m/s²

Remember !

If the speed is decreasing with time then accerlation is negative. negative accerlation is called retardation.

now, using Newton's Second Law of motion .i.e.,

➠ F = ma

➠ F = (13)(2.28)

➠ F = 29.64 N${.}$

thus, the force acting on the object is 29.64N

Answer 2

Given :-  

As per the given data ,

• Mass of the object(m) = 13 kg
• Initial velocity (u) = 20 m/s
• Final velocity (v) = 12 m/s
• Time taken (t) = 3.5 s

How to solve :-

• First we need to find the acceleration of the object in order to do that simply use the first equation of motion .
• Then , simply apply the Newton's second law in order to find force .

Solution : -

As per first equation of motion ,

➜   v = u + at

On rearranging ,

➜  a = v - u / t

➜  a = 20 - 12 / 3.5

➜  a = 8 / 3.5

➜  a = 2.28 m/s²

As per the Newton's second law of motion ,

➜  F = ma

➜  F = 13 x 2.28

➜  F = 29.64 N

The force exerted on a 13 kg object is 29.64 N