A man weights 70 kg. He stands on a weighing scale in a lift which is

1.	A man weights 70 kg. He stands on a weighing scale in a lift which is moving.1. upward with a uniform speed of 10 m/s.2. downward with an uniform acceleration of 5 m/s2.3. upward with an uniform accelerate of 5 m/s2. (Take g = 10m/s2). Find weight in each case.
Answer» 1. Weight W = mg = 70 × 10 = 700 N. 2. W = mg – ma = 70 × 10 – 70 × 5 = 700 – 350 = 350 N 3. W = mg + ma = 70 × 10 + 70 × 5 = 700 + 350 = 1050N. This question is based on the concept of g_effi.e. the effective g. In such questions, go in the frame of the lift and find g_effand then solve like a normal ground frame question by using g_effinstead of g. 1) As the lift is moving with a constant velocity, it already is an inertial frame and so g_eff= g So, weight = 7010 = 700 N 2) In the frame of lift, g_eff= 10-5 = 5 So, weight = 705 = 350 N 3) In the frame of lift, g_eff= 10+5 = 15 So, weight = 70*15 = 1050 N Hope it helps Ask if any doubt

A man weights 70 kg. He stands on a weighing scale in a lift which is moving.1. upward with a uniform speed of 10 m/s.2. downward with an uniform acceleration of 5 m/s2.3. upward with an uniform accelerate of 5 m/s2. (Take g = 10m/s2). Find weight in each case.

Answer»

1. Weight W = mg

= 70 × 10 = 700 N.

2. W = mg – ma

= 70 × 10 – 70 × 5

= 700 – 350

= 350 N

3. W = mg + ma

= 70 × 10 + 70 × 5

= 700 + 350

= 1050N.

This question is based on the concept of g_effi.e. the effective g. In such questions, go in the frame of the lift and find g_effand then solve like a normal ground frame question by using g_effinstead of g.

1) As the lift is moving with a constant velocity, it already is an inertial frame and so g_eff= g

So, weight = 70*10 = 700 N

2) In the frame of lift, g_eff= 10-5 = 5

So, weight = 70*5 = 350 N

3) In the frame of lift, g_eff= 10+5 = 15

So, weight = 70*15 = 1050 N

Hope it helps

Ask if any doubt

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