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JEE PHYSICS MCQ: LAWS OF MOTION

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Given below are two statements:

Statement I: An elevator can go up or down with uniform speed when its weight is balanced with the tension of its cable.

Statement II: Force exerted by the floor of an elevator on the foot of a person standing on it is more than his/her weight when the elevator goes down with increasing speed.

In the light of the above statements, choose the correct answer from the options given below:

View answer and explanation

Correct option: A

Statement I is true but Statement II is false

Option A is correct. Statement I is true because at uniform speed, acceleration is zero, so tension balances weight. Statement II is false because when going down with increasing speed, the net force is downwards, so the force exerted by the floor is less than the person's weight.

More Questions from LAWS OF MOTION

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A machine gun has a mass

5 {~kg}

. It fires 50 gram bullets at the rate of 30 bullets per minute at a speed of

400 {~ms}^{-1}

. What force is required to keep the gun in position? A particle of mass

4 {~m}

which is at rest explodes into three fragments. Two of the fragments each of mass

m

are found to move with a speed of

v

each in mutually perpendicular direction. The total energy released in the process is A block of mass ‘m’ rests on a rough inclined plane making an angle

30^\circ

with the horizontal. The co-efficient of static friction between the block and the plane is 0.8. If force of friction on the block is 10 N, the mass of the block is

\left( {g = 10\,m{s^{ - 2}}} \right).

Statement-1: A shell at the origin explodes into three pieces of masses

1 \mathrm{~kg}, 2 \mathrm{~kg}

m \mathrm{~kg}

1 \mathrm{~kg}

2 \mathrm{~kg}

pieces fly off with speeds

12 \mathrm{~m} / \mathrm{s}

x

8 \mathrm{~m} / \mathrm{s}

y

-axis respectively. If

{m} \,\mathrm{kg}

piece flies off with speed

40 \mathrm{~m} / \mathrm{s}

, the total mass of the shell must be

3.5 \mathrm{~kg}

.
Statement-2: The law of conservation of linear momentum holds good. For a system to follow the law of conservation of linear momentum during a collision , the condition is
Total external force acting on the system is zero.
Total external force acting on the system finite and time of collision is negligible.
Total internal force acting on the system is zero. If force on a rocket having exhaust velocity of

300 \mathrm{~m} / \mathrm{sec}

is 210 N, then rate of combustion of the fuel is: