Question

The apparent weight of a mass in a lift moving up is 80kg when its weight in the stationary lift is 60kg . If the same lift now moves up with same retardation , the weight of the mass will be what?

Answer 1

Answer:

Explanation:

The answer is 4kg. The explanation is given in the attachment...

Answer 2

$\huge{\mathfrak{\red{\underline{Solution :-}}}}$

→ Apparent weight = 80 kg

So,

→ m(g + a) = 80 kg ...........[1]

→ mg = 60 kg ..........[2]

→g = 10m/s

Put this value in equation 2.

» m(10) = 60

» m = 60/10

» m = 6kg

$\rule{200}{2}$

Put value of m and g in eqution 1.

» 6(10 + a) = 80

» 60 + 6a = 80

» 6a = 80 - 60

» 6a = 20

» a = 20/6

$\bf{a \: = \frac{{ \cancel20}}{{ \cancel6}} } \\ \\ \bf \: a \: = \frac{10}{3}$

We know that, when something is lifted there is retardation.

So,

» m[g +(-a)]

________________[Put Values]

$\bf6(10 + \frac{ - 10}{3}) \\ \\ \bf{6(10 - \frac{10}{3})} \\ \\ \mathfrak{Taking \: LCM} \\ \\ \bf6( \frac{30 - 10}{3}) \\ \\ \bf{\cancel6}\times \frac{20}{{ \cancel3}} \\ \\ \bf{ \huge{40N}}$

We know that,

$\bf{ \cancel40 }\times \frac{{ \cancel1}}{10} \: kg \\ \\ \bf{ \huge{ \boxed{ \pink{4 \: kg}}}}$