Question

1)man of mass 70 kg stands on weighing scale in a lift which is moving. now find when the lift moves :-

(a) upwards with a uniform speed of 10 m s–1

(b) downwards with a uniform acceleration of 5 m s–2

Answer 1

⭕️Let's take g = 10 for convenient calculation.

(a) Mass of the man, m = 70 kg

Acceleration, a = 0

⭕️Using Newton’s second law of motion :-

R – mg = ma

⭕️m × a is the net force acting on the man.

⭕️As the lift is moving at a uniform speed, acceleration a = 0

∴R = mg

= 70 × 10

= 700 N

∴ Reading on the weighing scale we will get :-

= 700/g

=700/10

=70 Kg


(b) Mass of the man, m = 70 kg

Acceleration, a = 5 m/s² downward.

⭕️Using Newton’s second law of motion :-

R + mg = ma

R = m(g – a)

= 70 (10 – 5) = 70 × 5

⇒∴ 350 N

∴ Reading on the weighing scale =

=350/g

=350/10

⇒ ∴ 35 Kg


$\huge\bf{\boxed {\red{\mathfrak{thank \: you :)}}}}$

Answer 2

$\huge\mathfrak\red{Answer :}$


a) According to question we have given;

m = 70 kg

a = 0 m/s²

R = ?

Now,

R - mg = ma

R = ma + mg

R = m (a + g)

R = 70 (0 + 10)

[As we know g = 10]

R = 70 × 10

R = 700 N

Now, when we check it on weighing machine we got...

700/10 = 70 kg


b) a = 5 m/s²

m = 70 kg

R = ?

R = mg - mg

R = m (g - a)

R = 70 (10 - 5)

R = 70 × 5

R = 350 N

When we read it on weighing machine... we got

350/10 = 35 kg

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