Question

The mass of an elevator is 4000 kg. The tension in the cable is 56 kN. Starting from the ground floor,
how much distance will it rise in 2s?
(A) 2m (B) 4m (C) 8m (D) 16m

Answer 1

Answer:

T=mg+ma

T=m(g+a)

48000=4000(g+a)

12=g+a=10+a

⇒ a = 2ms

−2

S=vt+

2

1

at

2

S=0+

2

1

×2×(3)

2

=9m

Answer 2

Answer:

the elevator is raised by 8.4 m ✔✔

Explanation:

Mass of elevator = 4000 kg

Weight of elevator = Mass × gravity

Weight = 4000 × 9.8

Weight = 39200 N

Upward Force applied = 56000 N

F(net) = 56000 - Weight

F(net) = 56000 - 39200

F(net) = 16800 N

Also, F(net) = mass (m) × acceleration (a)

a = F(net) /m

a = 16800/4000

a = 4.2 m/s²

Now,

Initial velocity (u) = 0 m/s

Time = 2 seconds

H = ?

H = ut + ½ at²

H = 0 + 4.2×2×2×½

H = 8.4m

Hence, the elevator is raised by 8.4 m.

may be the option is (C) , approximately 8 m