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If the unit of force were kilo newton, that of time millisecond and that of power kilowatt, what should be the units of mass in kg?

Answer
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Hint: In the given question, we can calculate the unit of mass by using the formula of power and putting all the given values in it. After this, we will get the value of length and put it in Newton's 2nd law of motion for the unit of mass.

Complete Solution:
Given: Force, F = kN = 103N
Time, t=Milliseconds =103s
Power, P=kW = 103W

We need to find the units of mass in kg.

Now, we know

Power=EnergyTime=Force×DisplacementTime

Putting all the values in above equation,

103W=103N×L103s
L=103m

Now, to find the units of mass in kg we will use the relation,

Force=Mass×Acceleration

F=M×a
F=M×vt
F=M×dt×t

Here, we can take d=L
F=MLt2
Put all the values in above equation, we get

103N=M×(103m)(103s)2
M=103N×(103s)2103m

M=1kg

Hence, the units of mass is in kg.

Note: Alternative Method:
We can also solve this question by using dimensional analysis.
We know, dim P= [ML2T1] and ….eq i)
dim F=[MLT2]
F2=[MLT2]2 ….eq ii)
Now divide eq i) and eq ii),
PF2=ML2T1M2L2T4
PF2=T3M
M=F2T3P
Put all the values in above equation, we get
M=(103)2(103)3103
⇒M= 1kg
Therefore, the unit of mass is in kg.
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