physics test 2

Boxes A and B are in contact on a horizontal, firctionless surface. Box A has a mass of 20 kg and box B has a mass of 5 kg. A horizontal force of 250 N is exerted on box A. What is the magnitude of the force that box A exerts on box B?

F=50 N

A 15 N force is applied to a spring with spring constant 300 N/m. How much work was required to stretch the spring?

0.375 J

A 6 kg box slides across a horizontal frictionless surface at 3 m/s. If the box runs into a spring with force constant 75 N/m, what is the maximum distance the spring compresses?

0.85 m

A 1.5 kg book is sliding along a rough horizontal surface. At point A the book is moving at 3.21 m/s. At point B the book is moving at 1.25 m/s.a)How much work was done on the book between A and B?b)What would be the velocity of the book at point C if -0.75 J of work was done to the book between point B and point C?

a)-6.56 Jb)0.75 m/s

A 75 kg painter climbs a ladder that is 2.75 m long and leans against a vertical wall at anangle of 30º with the wall.a)How much work does gravity do on the painter?b)Does the answer to part (a) depend on whether the painter climbs at constant speed of accelerates up the ladder? Explain.

a)1750 J b)No. Gravitational potential energy is a function of height and mass only.

Adult cheetahs, the fastest big cat, have a mass of about 70 kg and have been measured to run at about 32 m/s (72 mph).a)What is the kinetic energy of such a cheetah?b)If the speed of the cheetah were doubled, by what factor would the kinetic energy change?

a)35840 J b)4 (quadrupled)

A chair of mass 12 kg is sitting on a horizontal frictionless floor. You push on the chair with a force F=40 N that is directed at an angle of 37° below the horizontal and the chair slides across the floor.a)What is the normal force on the chair from the floor?b)What is the acceleration of the chair?

a)N=142 Nb)2.7 m/s2

An adventurous archaeologist crosses between two rock cliffs by slowly going hand overhand along a rope stretched between the cliffs. He stops to rest at the middle of the rope. The rope will break if the tension in the rope exceeds 2.5x104 N. The mass of the archaeologist is 90 kg.a)If the angle from the horizontal is 10°, what is the tension in the rope?b)What is the smallest angle from the horizontal that the rope can have for the rope tonot break?

a)T=2540 Nb)θ=1°

A massless rope is attached to a block with mass 4 kg that rests on a frictionless, horizontal surface. The horizontal rope passes over a frictionless, massless pulley, and is attached to a block with mass m which is hanging. When the blocks are released, the tension in the rope is 15 N.a)What is the acceleration of the blocks?b)Find m.

a)a=3.75 m/s2b)m=2.5 kg

Three sleds with mass m are being pulled horizontally on a frictionless horizontal ice surface using ropes. That is, the first sled is pulled by rope, the first sled is attached to the second sled by another rope, and the second sled is attached to the third sled by a third rope. The first sled is being pulled with a force of 190 N.a)What is the acceleration of the sleds?b)What is the tension in the rope pulling the second sled?c)What is the tension in the rope pulling the third sled?

a)a=63/m m/s2b)T=127 Nc)T= 63 N

How many joules of energy does a 100 W light bulb use in 3600 s?

360000 J

A branch falls from the top of a 95 m tall redwood tree. Using conservation energy, how fast is the branch moving when right before it hits the ground?

43 m/s

A 12 kg sled moves in a straight line on a frictionless horizontal surface. At one point, the sled has a speed of 4 m/s. After the sled moves 2.5 m, the speed of the sled is 6m/s. What force was applied to the sled to increase its speed?

48 N

A 520 N force is used to stretch a spring 0.2 m. What is the potential energy of the spring?

52 J

A 75 kg mountain climber ascends from the 1500 m level to the top at 2400 m. What is his change in gravitational potential energy

662000 J

World class sprinters can accelerate out of the starting blocks with an acceleration that isnearly horizontal and has magnitude 15 m/s2. How much horizontal force must a 55 kg sprinter exert on the starting blocks to produce this acceleration?

F=825 N

A 100 N object is suspended from two massless ropes that are attached to the ceiling. The rope to the right makes an angle of 30° to the ceiling and the rope to the left makes an angle of 45° to the ceiling. What are the tensions in the rope?

TR=73.4 N, TL=89.5 N

A stockroom worker pushes a box with mass 16.8 kg on a horizontal surface with a constant speed of 3.5 m/s. The coefficient of kinetic friction between the box and the surface is 0.2. What horizontal force must the worker apply to the box to maintain the constant velocity?

f=33 N