Physics Review 2
Doug hits a hockey puck, giving it an initial velocity of 6.0 m/s. If the coefficient of kinetic friction between the ice and puck is 0.050, how far will the puck slide before stopping?
-M(mg)=ma -(0.05)(m)(9.8)=ma -0.49 m/s^2= a v^2/2a= 6^2/(2 x .49)= 36.7m
A 5000N weight is held suspended in equilibrium by two cables. Cable 1 applies a horizontal force to the right of the object and has a tension, T1. Cable 2 applies a force upward and to the left at an angle of 37 degrees to the negative x-axis and has a tension, T2. What is the tension, T1?
1.) T2sin37=5000N T2=8308.2 2.) T1= 8308.2cos37= 6635N
There are six books in a stack, each with a weight of 5.0 N. The coefficient of friction between all the books is 0.20 as is the coefficient between the table and the bottom book. What horizontal push must I just exceed on the next bottom book to start sliding the top 5 books off the bottom one?
25N x 0.2= 5.0N
Samantha pushes a 50N crate up a ramp 25m in length and inclines at 10 degrees with the horizontal. What potential energy change does the crate experience?
25sin10= 4.34 m (height she goes up) 4.34m x 50N= 217 J
A horizontal force of 200N is applied to a 55kg cart across a 10m level surface. If the cart accelerate at 2.0 m/s^2, then what is the work don't by the force of friction as it acts to retard the motion of the cart?
55kg x 2m/s^2= 110N 110N-200N= -90N (due to friction) w=Fd w= -90N x 10m w= -900J
A 7kg bowling ball falls from a 2.0m shelf. Just before hitting the floor, what will be its kinetic energy?
7kg x 9.8 m/s^2 x 2m= 137J
An airplane of mass 1.2x10^4 kg tows a glider of mass 0.6x10^4 kg. The airplane propellers provide a net forward thrust of 3.6x10^4. What is the glider's acceleration?
F=ma 3.6x10^4= (1.2x10^4+0.6x10^4)a a=2.0 m/s^2
The acceleration due to gravity on the moon's surface is one-sixth that on earth. What net force would be required to accelerate a 20kg object at 6.0m/s^2 on the moon?
F=ma F=20x 6 F=120 N
A block mass 5kg rests on a horizontal surface where the coefficient of kinetic energy between the two is 0.200. A string attached to the block is pulled horizontally, resulting in a 2.00 m/s^2 acceleration by the block. Find the tension of the string.
F=ma F=m(Mg+a) F= 5kg (0.2x9.8 + 2) F= 19.8 N
A box is to be moved across a level surface. A force magnitude 200N may be applied at an angle of 30 degrees below the horizontal to push the box or at an angle of 30 degrees above the horizontal to pull the box, either application sufficient to overcome friction and move the box. Which application will cause the box to have the greater acceleration?
The one above the horizontal, because its vertical component(pull) reduces kinetic friction.
Two ropes are attached to a 40kg object. The first rope applies a force of 25N and second, 40N. If the two ropes are perpendicular to each other, what is the resultant acceleration of the object?
a^2+b^2=c^2 25^2 + 40^2= c^2 c= 47.17 F=ma 47.17=40a a= 1.2 m/s
A ball is rolled horizontally off a table with an initial speed of 0.24 m/s. A stopwatch measure the ball's trajectory time form the table to the floor to be 0.30s. What is the height of the table?
d= 1/2gt^2 d= 1/2(9.8)(0.30^2) d=0.44m
As I slide a box at constant speed up a frictionless slope, pulling parallel to the slope, the tension in the rope will be:
less than the weight of the box; pull cancels weight
A box of mass m is placed on an incline with an angle inclination x. The box does not slide. The magnitude of the frictional force in this case is: (equation)
mgsinx
A horizontal force of 100N is applied to move a 45kg cart across a 9.0m level surface. What work is done by the 100N force?
w=Fd w=100x9 w=900 J
