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Friction – Numerical Problem

A block of mass 1 kg lies on a horizontal surface in a truck . The coefficient of static friction between the block and the surface is 0.6 .if the acceleration of the truct is 5m/s² calculate the frictional force acting on the block.

motion_friction1_240Asked  Mrinmoy Das

Newton’s 2nd Law, 2 Crates held by a Pulley

Two crate A and B are connected with a rope with negligible mass over a frictionless pulley as represented below. The crates are at rest. Crate A has an unknown mass and hangs vertically to the right of the slope and crate B with mass 22 kg, hangs on the slope to the left. The slope makes and angle of 67 degrees with the horizontal. The static coefficient of friction between crate B and the surface of the slope is 1.716. The frictional force is up the slope.”

The Answer is suppose to be 5.5Kg, but I don’t know how to get it.
Please Help


Asked Greg Sithole


Work Energy Problem

A 2kg hammer with a speed of 40m/s strikes a 100g nail driving it into a wooden block. If there is no dissipation of energy in this process and the frictional force applied by the wooden block is 8000N, how deep would be nail penetrate into the block?

Asked Jaisy

Does light experience friction?

Does light experience friction?

Asked rashmi (VIII B, KV AFS Bidar)


Night Light

FRICTION  is defined as the force which opposes relative motion between two surfaces in contact.

If you mean friction in the normal sense as above (as discussed in class), then the answer is “NO“.

Light is a form of energy and not a particle. But it is true that light shows some particle behaviour also.

But, there is a slowing down when light interacts with matter. But, in a homogeneous medium, light has a constant speed. The speed of light is different in different medium.  If we go to the atomic or molecular picture of matter, then we can imagine that light is interacting with a molecule, during the time of interaction, the light can be assumed to have been absorbed by the particle and then it is re-radiated. the re-radiated light travels to the next atom and interacts/absorbed. this slows down the average speed of light, but is constant for a particular homogeneous medium.

The speed of light is maximum in vacuum where there is no matter for light to interact.

So, in between two atoms also, light travels with its branded 3L kmps speed.

Also refer:

  1. http://phasing.org/2009/09/25/does-light-have-friction/
  2. http://answers.yahoo.com/question/index?qid=20100425222814AA2LUvq

More questions waiting for answers:

The following questions are waiting for an answer. You can contribute your answers by the time our team answer them.

  • When a piece of paper is held with its face perpendicular to a uniform electric field the flux through it is 25.0 N·m2/C. When the paper is turned 25.0o with respect to the field the flux through it is?
  • A cylinder rests on a horizontial rotating  disc, find at what angular velocity the axes of the disc and cylinder is R and the coefficient of friction U>D/H, where D is the diameter of the cylinder and H is its height.
  • Can static friction do non zero work on an object?if yes give example . if no give reason
  • How angular momentum is different from linear momentum?


Body at incline

A free body diagram of a mass on an inclined plane

1. In first case we have the box with weight, say, 10 Newtons on incline. We calculate two components (perpendicular and parallel)of weight. We calculate normal force and force of friction. The box is at rest.

2. In second case we have ball on incline, made of same material as box from first case. Weight of the ball is the same as in first case, components of weight are the same as in first case. Normal force and friction have the same amount as in the case of box. But,unlike the box, ball is moving – it slides down. How’s that possible? If calculated net force is zero?

 Petar asked


It is not true that the ball slides,  but it will roll down.

In the first case, the forces balance each other and there is no motion.

In the second force, the frictional force acting tangentially backwards (up the incline) and the component of weight of the ball acting parallel to the plane and through the centre of the ball constitute a couple and tends to rotate it. Now there is no sliding; it rolls.

(If any further clarification is required please post as comment to this post)

Please refer to http://www.real-world-physics-problems.com/rolling-without-slipping.html for detailed treatment of the Physics of rolling without friction.

Physics Numerical Problem

A small mass of 10 KG is suspended from a spring balance. It is Pulled by Horizontal Spring so it makes 60º with the vertical. Find the new reading of the spring balance.

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