Chapter 4 Physics Test
A 0.150 kg base ball is thrown upward with an initial speed of 20.0 m/s. a. What is the force on the ball when it reaches half of its maximum height? (Disregard air resistance.) b. What is the force on the ball when it reaches its peak?
-mg
The net force on a golf cart is 390 N north. If the cart has a total mass of 270 kg, what are the magnitude and direction of the cart's acceleration?
1.4 m/s2 north
The net force on the propeller of a 3.2 kg model airplane is 7.0 N forward. What is the acceleration of the airplane?
2.2 m/s^2
Acarhasamassof1.50×103kg.Iftheforceactingonthecaris 6.75 × 103 N to the east, what is the car's acceleration?
4.50 m/s2 east
The student in item 1 moves the box up a ramp inclined at 12° with the horizontal. If the box starts from rest at the bottom of the ramp and is pulled at an angle of 25.0° with respect to the incline and with the same 185 N force, what is the acceleration up the ramp? Assume that mk = 0.27.
Fg,y = mg(cos q1) Fg,x = mg(sin q1) Fapplied,x = Fapplied(cos q2) Fapplied,y = Fapplied(sin q2) Fn = Fg,y − Fapplied,y Fk =mkFn Fapplied,x − Fk − Fg,x ax=fapplied-fk-fg,x/ m
A box of books weighing 325 N moves at a constant velocity across the floor when the box is pushed with a force of 425 N exerted downward at an angle of 35.2° below the horizontal. Find mk between the box and the floor.
Fk = Fapplied,x = Fapplied(cos q) Fn = Fg − Fapplied,y = Fg − Fapplied (sin q) mk=fk/fn =.609
A 5.4 kg bag of groceries is in equilibrium on an incline of angle q = 15°. Find the magnitude of the normal force on the bag.
Fn = mg(cos q)
A student pulls on a rope attached to a box of books and moves the box down the hall. The student pulls with a force of 185 N at an angle of 25.0° above the horizontal. The box has a mass of 35.0 kg, and mk between the box and the floor is 0.27. Find the acceleration of the box.
Fn= mg − Fapplied(sin q) Fk = mkFn Fx, net= Fapplied(cos q) − Fk a= fx,net/m 2.7 m/s^2
A man is pulling on his dog with a force of 70.0 N directed at an angle of +30.0° to the horizontal. Find the x and y components of this force.
Fx = F(cos q) = (70.0 N)(cos 30.0°) = 60.6 N Fy = F(sin q) = (70.0 N)(sin 30.0°)= 35 N
Explain the relationship between mass and weight.
Mass is a measure of the inertia of an object; weight is a measure of the force of gravity acting on an object
An object thrown into the air stops at the highest point in its path. Is it in equilibrium at this point? Explain.
No because gravitational force is still acting on the object.
If an object is at rest, can we conclude that no external forces are acting on it?
No, gravity is still acting on it.
An astronaut on the moon has a 110 kg crate and a 230 kg crate. How do the forces required to lift the crates straight up on the moon compare with the forces required to lift them on Earth? (Assume that the astronaut lifts with constant velocity in both cases.)
Since gravity on the moon is 1/6 the gravity on earth, the force to lift the crates on the moon will be 1/6 th of the forces needed on the earth.
State Newton's second law in your own words.
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
A teapot is initially at rest on a horizontal tabletop, then one end of the table is lifted slightly. Does the normal force increase or decrease? Does the force of static friction increase or decrease?
The normal force decreases. The static friction increases.
Is it possible for an object to be in motion if no net force is acting on it? Explain.
Yes, when the acceleration is zero and the velocity constant.
A 75 kg box slides down a 25.0° ramp with an acceleration of 3.60 m/s2. a. Find mk between the box and the ramp. b. What acceleration would a 175 kg box have on this ramp?
a Fn = Fg,y = mg(cos q) fk= mg(sin q)−ma uk=fk/ fn =0.061 b. ax = g(sin q − mk cos q) =3.61 m/s2 down the ramp
A museum curator moves artifacts into place on various different display surfaces. Use the values in Table 2 to find Fs,max and Fk for the following situations: a. moving a 145 kg aluminum sculpture across a horizontal steel platform b. pulling a 15 kg steel sword across a horizontal steel shield c. pushing a 250 kg wood bed on a horizontal wood floor d. sliding a 0.55 kg glass amulet on a horizontal glass display case
a. b. c. d.
If the basket in item 25 has a mass of 5.5kg, find the magnitude of the normal force for the situations described in (a) through (d).
a. Fn = mg b. Fn = mg(cos q) c. Fn = mg(cos q) d. Fn = mg(cos q)
The wind exerts a force of 452 N north on a sailboat, while the water exerts a force of 325 N west on the sailboat. Find the magnitude and direction of the net force on the sailboat.
arctan (y/x)= 54.3° north of west, or 35.7° west of nor fnet= 557 N
A gust of wind blows an apple from a tree. As the apple falls, the gravita- tional force on the apple is 2.25 N downward, and the force of the wind on the apple is 1.05 N to the right. Find the magnitude and direction of the net force on the apple.
arctan(X/Y) = 25.0° counterclockwise from straight down
The force that attracts Earth to an object is equal to and opposite the force that Earth exerts on the object. Explain why Earth's acceleration is not equal to and opposite the object's acceleration.
its mass is so great that the same force will not make the acceleration equal
A 25 kg chair initially at rest on a horizontal floor requires a 165 N hori- zontal force to set it in motion. Once the chair is in motion, a 127 N hor- izontal force keeps it moving at a constant velocity. a. Find the coefficient of static friction between the chair and the floor. b. Find the coefficient of kinetic friction between the chair and the floor.
m = Fs, max/ mg .67 uk=fk/mg .52
Once the crate in Sample Problem D is in motion, a horizontal force of 53 N keeps the crate moving with a constant velocity. Find mk, the coeffi- cient of kinetic friction, between the crate and the floor.
m = fk/mg .23
A soccer ball kicked with a force of 13.5 N accelerates at 6.5 m/s2 to the right. What is the mass of the ball?
m=fnet/a 2.1 kg
What physical quantity is a measure of the amount of inertia an object has?
mass
Which is usually greater, the maximum force of static friction or the force of kinetic friction?
the maximum force of static friction
A 2.0 kg otter starts from rest at the top of a muddy incline 85 cm long and slides down to the bottom in 0.50 s. What net force acts on the otter along the incline?
∆x = .5a(∆t)2 14 N