Advertisements
Advertisements
प्रश्न
The force exerted by the floor of an elevator on the foot of a person is more than the weight of the person if the elevator is
(a) going up and slowing down
(b) going up and speeding up
(c) going down and slowing down
(d) going down and speeding up
उत्तर
(b) going up and speeding up
(c) going down and slowing down
It means normal force exerted by the floor of the elevator on the person is greater that the weight of the person.
i.e. N > mg
(i) Going up and speeding up:
aeff = g + a
N = maeff = mg + ma (N > mg)
(ii) Going down and speeding up:
aeff = g – a
N = mg – ma (N < mg)
(iii) Going down and slowing down:
aeff = g – (–a) = g + a
N = mg + ma (N > mg)
(iv) Going up and slowing down:
aeff = g – a
N = mg – ma (N < mg)
APPEARS IN
संबंधित प्रश्न
A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because ______.
Give the magnitude and direction of the net force acting on a drop of rain falling down with a constant speed.
The driver of a three-wheeler moving with a speed of 36 km/h sees a child standing in the middle of the road and brings his vehicle to rest in 4.0 s just in time to save the child. What is the average retarding force on the vehicle? The mass of the three-wheeler is 400 kg and the mass of the driver is 65 kg.
Name the physical quantity whose unit is ‘newton’.
Name the law involved in the following situation :
if there were no friction and no air resistance, then a moving bicycle would go on moving for ever.
Is it possible for a particle to describe a curved path if no force acts on it? Does your answer depend on the frame of reference chosen to view the particle?
The figure shows a light spring balance connected to two blocks of mass 20 kg each. The graduations in the balance measure the tension in the spring. (a) What is the reading of the balance? (b) Will the reading change if the balance is heavy, say 2.0 kg? (c) What will happen if the spring is light but the blocks have unequal masses?
A reference frame attached to the earth
(a) is an inertial frame by definition
(b) cannot be an inertial frame because the earth is revolving around the sun
(c) is an inertial frame because Newton's laws are applicable in this frame
(d) cannot be an inertial frame because the earth is rotating about its axis.
A block of mass 2 kg placed on a long frictionless horizontal table is pulled horizontally by a constant force F. It is found to move 10 m in the first seconds. Find the magnitude of F.
If you jump barefoot on a hard surface, your legs are injured. But they are not injured if you jump on a soft surface like sand or pillow. Why?
When a train starts, the head of a standing passenger seems to be pushed backward. Analyse the situation from the ground frame. Does it really go backward? Coming back to the train frame, how do you explain the backward movement of the head on the basis of Newton's laws?
Give qualitative definition of force on the basic of Newton's first law of motion.
A force of 600 dynes acts on a glass ball of mass 200 g for 12 s. If initially, the ball is at rest, find
- Final velocity
- Distance covered.
The greater is the __________ the greater is the inertia of an object.
What do you mean by inertia of rest?
Differentiate between gravitational mass and inertial mass.
Block A of weight 100 N rests on a frictionless inclined plane of slope angle 30° (figure). A flexible cord attached to A passes over a frictonless pulley and is connected to block B of weight W. Find the weight W for which the system is in equilibrium.
The masses of 10 kg and 20 kg, respectively, are connected by massless spring as shown in the figure. A force of 200 N acts on the 20 kg mass. At the instant shown, the 10 kg mass has acceleration of 12 m/s2. What is the acceleration of 20 kg mass?
(g = 10 m/s2)
