Advertisements
Advertisements
Question
A man of mass 70 kg stands on a weighing scale in a lift which is moving
- upwards with a uniform speed of 10 m s-1
- downwards with a uniform acceleration of 5 m s–2
- upwards with a uniform acceleration of 5 m s–2. What would be the readings on the scale in each case?
- What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?
Advertisements
Solution
Here, m = 70 kg, g = 10 m/s2
In each instance, the weighing machine measures the reaction R, which represents the apparent weight.
(a) When the lift moves upwards with a uniform speed, acceleration a = 0.
R = mg = 70 x 10 = 700 N
(b) When the lift moves downward with a = 5 ms-2
R = m (g - a) = 70 (10 - 5) = 350 N
(c) When the lift moves upwards with a = 5 ms-2
R = m (g + a) = 70 (10 + 5) = 1050 N
(d) If the lift were to come down freely under gravity, downward acceleration. a = g
∴ R = m (g - a) = m (g - g) = zero.
APPEARS IN
RELATED QUESTIONS
A batsman deflects a ball by an angle of 45° without changing its initial speed which is equal to 54 km/h. What is the impulse imparted to the ball? (Mass of the ball is 0.15 kg.)
When a horse pulls a cart, the force that helps the horse to move forward is the force exerted by
Two objects A and B are thrown upward simultaneously with the same speed. The mass of A is greater than that of B. Suppose the air exerts a constant and equal force of resistance on the two bodies.
The figure shows the displacement of a particle going along the X-axis as a function of time. The force acting on the particle is zero in the region
(a) AB
(b) BC
(c) CD
(d) DE
If the tension in the cable supporting an elevator is equal to the weight of the elevator, the elevator may be
(a) going up with increasing speed
(b) going down with increasing speed
(c) going up with uniform speed
(d) going down with uniform speed
Two blocks of equal mass m are tied to each other through a light string. One of the blocks is pulled along the line joining them with a constant force F. Find the tension in the string joining the blocks.
A small block B is placed on another block A of mass 5 kg and length 20 cm. Initially, the block B is near the right end of block A (In the following Figure). A constant horizontal force of 10 N is applied to the block A. All the surfaces are assumed frictionless. Find the time that elapses before block B separates from A.
Suppose the ceiling in the previous problem is that of an elevator which is going up with an acceleration of 2.0 m/s2. Find the elongation.
In the previous problem, suppose m2 = 2.0 kg and m3 = 3.0 kg. What should be the mass m, so that it remains at rest?
Find the acceleration of the 500 g block in the following figure.
A block is kept on the floor of an elevator at rest. The elevator starts descending with an acceleration of 12 m/s2. Find the displacement of the block during the first 0.2 s after the start. Take g = 10 m/s2.
Define linear momentum and state its S.I. unit.
Write the mathematical form of Newton's second law of motion. State the conditions if any.
The unit of linear momentum is :
How long will a stone take to fall to the ground from the top of a building 80 m high
What do you understand by the term momentum?
What do you mean by linear momentum of a body?
State Newton's second law of motion. Is Newton's first law of motion contained in Newton's second law of motion?
According to Newton's Second Law of Motion, what quantity is directly proportional to the applied force?
