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Friction – a numerical

a force of 20 N is applied parallel to the surface of a horizontal table is just sufficient to make a block of mass 4.kg move on the table calculate the coefficient of friction between the block and the table

Numerical Problem from Laws of Motion

An 8000 kg engine pulls 40000 kg train alonged a level track and gives an acceleration of 1.2m/s2. Find the accelaration produced by same engine on a train of mass 16000kg?

Answer:

Force exerted by the engine = mass of train x acceleration =  40000 x 1.2=48000N

When the same engine pulls a 16000 kg train, the acceleration = 48000/16000=3m/s2

A few numerical problems from laws of motion

  1. A worker pulls a 200. N packing crate with an applied force of 55.0 N.  The crate accelerates at a rate of 0.250  m/s(squared).  What is the coefficient of kinetic friction between the crate and the factory floor?
  2. A student pulls a 150. N sled up a 28 degree slope at a constant speed by applying a force of 100. N.  Near the top of the hill he releases the sled.  With what acceleration does the sled go down the hill?
  3. A 200. N crate rests on a ramp; the maximum angle just before it slips is 25 degrees with the horizontal.  What is the coefficient of static friction between the crate and the surface of the ramp?
  4. A man pulls a sled with a weight of 200. N with a constant velocity across a horizontal snow surface.  If a force of 80N is being applied to the sled rope at an angle of 53 degrees to the ground, what is the coefficient of friction between the sled and the ground?
  5. A jet plane is flying with  a constant speed along a straight line at an angle of 30degree  above the horizontal. The weight of plane is 86 500N. Its engine provides a forward thrust T of 103 000N. The lift of force L(directed perpendicular to the wings)and the force R of air resistance (directed opposite to the motion)act on the plane. Find L & R

An interesting numerical problem from kinematics

George’s favorite food was bananas. One day he was walking with his friend, the man in the yellow hat, as he was eating a banana. They were in New York City and they were walking up the Empire State Building. Finally they made it to the top! George spied a nice young woman walking down 5th avenue balancing this hat on her head.  She was very noticeable for she was six feet tall! George, being the troublemaker he was, wanted to see if he could drop his banana peel in her hat. He noticed that she was jogging at a constant pace of 6 miles per hour. George was on the 102nd floor observatory, which is 1,224 feet from the ground.*
Assuming that George lands the banana peel in the hat……..
A)      How long will the banana peel be in the air? (Assuming there is no wind and the banana will drop straight down from the empire state building)
B)      What will the velocity of the banana peel be right before it lands in the woman’s hat?
C)      How far away must the woman’s hat be from the landing point of the banana peel (horizontally) when George makes his scandalous move and drops the peel.
D)      If George decides to throw another peel one second later to land it on the ground and trip the jogger, at what velocity must he throw it at so that it hits the ground at the same the original peel lands in the hat.

Numerical from centre of mass

Two skaters, one with Mass 45kg, 2’nd with Mass of 65kg stand on an ice rink holding a pole with L=10m with negligible mass. starting from the ends of the pole, the skaters pull themselves along the pole until they meet. How far does the 45kg skater move?
Hint: They will meet at the centre of mass of the system.

If the 45 kg skater moves by x m, then the second one travels (10-x)m

then,

45 x = 65(10-x)

Solve and get the value for x

Numerical from Kinematics and vectors

  1. A jetliner moving at 500. km/h due east moves into a region where the wind is blowing from exactly NW toward the SE at a speed of 127 km/h. What is the new velocity of the airplane? you must include both magnitude and direction in your answer.
  2. The speed of a train changes from36km/h to 72km/h in 10sec. calculate the distance travelled during this time

 

Kinematics Numerical

  1. A particle travels 20 m in 7th second and 24m in 9th sec. find initial velocity?
  2. in a projectile motion , a body thrown from the ground ,at what angle both the vertical height and range will be equal?
  3. The velocity v(cm/s) of a particle is given in terms of time t(in seconds) by the equation v = at+b/t+c. Dimension of a,b, and c are ?

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