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JEE PHYSICS MCQ: LAWS OF MOTION

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Understanding +4 | -1

You are pushing a wooden crate across the floor at a constant speed. You decide to change the orientation of crate such that area of contact with floor become half. In the new orientation, to push the same crate across the same floor with the same constant speed, the force that you apply must be about as the force required before you changed the crate's orientation.

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Correct option: C

Equally great

Option C (Equally great) is correct because the force required to push the crate at a constant speed depends on the kinetic friction, which is independent of the area of contact.

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: