Phys 220 Exam 1-2

What buoyant force does a 0.50 kg solid gold crown experience when it is immersed in water? The density of gold is 19.3 × 10^3 kg/m3 and that of water is 1000 kg/m3.

(.5/(19.3*10^3))*10^3*9.8 .25N

The fulcrum of a uniform 20 kg seesaw that is 4.0 m long is located 2.5 m from one end. A 42 kg child sits on the long end. Determine the mass a person at the other end would have to be in order to balance the seesaw.

(20*(2.5-4/2)+42*2.5)/(4-2.5) 77kg

The figure shows a graph of the velocity of an object as a function of time. What is the displacement of the object from 2.0 s to 8.0 s?

Add above y-intercept, subtract below 40 m

A golf ball of mass 0.050 kg is at rest on the tee. Just after being struck, it has a velocity of 102 m/s. If the club and ball were in contact for 8.1x10-4 s, what is the average force exerted on the ball by the club?

.05*102/.81 6.3 kN

A man in a gym is holding an 8.0 kg weight at arm's length, a distance of 0.55 m from his shoulder joint. What is the torque about his shoulder joint due to the weight if his arm is held at 30° below the horizontal?

.55*8*9.8*(sqrt(3)/2) 37 N ∙ m

A driver, traveling at 20 m/s, slows down her 2000 kg truck to stop for a red light. What work is done on the truck by the friction force of the road?

.5mv^2 = .5*2000*20^2 -4.0 x 10^5 J

A 1500 kg car moving at 22 m/s hits an initially uncompressed horizontal ideal spring with spring constant (force constant) of 1.5 × 106 N/m. What is the maximum distance the spring compresses?

.5mv^2 = .5kx^2 .5*1500*22^2 = .5(1.5*10^6)x^2 0.70 m

A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, and there is no appreciable air resistance. What is the speed of the bead at point C? 200-->160

.5mv^2i+mgh = .5mv^2f+mgh .5(20)^2+9.8*200 = .5v^2 + 9.8*160 34 m/s

How many moles are there in 2.00 kg of copper? The atomic weight of copper is 63.5 g/mol and its density is 8.90 g/cm3.

2.00kg = 2000g N = 2000/63.5 31.5

A 30.0 kg load is being held in place using massless wires in the ideal pulley arrangement shown in the figure. What is the magnitude of the force F?

30*9.8*.5=147 147 N

A truck is using a hook to tow a car whose mass is one quarter that of the truck. If the force exerted by the truck on the car is 6000 N, then the force exerted by the car on the truck is...

6000N

A ball is thrown at an initial speed of 8.0 m/s at an angle of 35° above the horizontal. If there is no air resistance, what is the speed of the ball when it returns to the same horizontal level?

8.0 m/s

Two small balls, A and B, attract each other gravitationally with a force of magnitude F. If we now double both masses and also double the distance of separation between the balls, what will be the magnitude of the attractive force on each one?

F

A 13,000 N vehicle is to be lifted by a 25 cm diameter hydraulic piston. What force needs to be applied to a 5.0 cm diameter piston to accomplish this? Assume the pistons each have negligible weight.

F1/A1=F2/A2 F1/r1^2=F2/r2^2 13,000/25^2=F2/5^2 520 N

A potter's wheel has the shape of a solid uniform disk of mass 7.0 kg and radius 0.65 m. It spins about an axis perpendicular to the disk at its center. A small 2.1 kg lump of very dense clay is dropped onto the wheel at a distance 0.41 m from the axis. What is the moment of inertia of the system about the axis of spin?

I=Mr^2 I=.5*7.0*.65^2 + 2.1*.41^2 = 1.8 1.8 kg ∙ m2

A uniform solid cylinder with a radius of 10 cm and a mass of 3.0 kg is rotating about its center with an angular speed of 33.4 rpm. What is its kinetic energy?

KE=.5IW^2 =.5(.5mr^2)w^2 .5(.5*3*.1^2)(33.4(2pi/60))^2 9.17*10^-2 0.092 J

What happens to the pressure and number of air molecules inside of a hot-air balloon when the air is heated? Assume that volume remains constant.

Pressure remains constant, number of air molecules decreases

A firecracker explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I. The total momentum of the fragments is equal to the original momentum of the firecracker. II. The total kinetic energy of the fragments is equal to the original kinetic energy of the firecracker.

Statement I only

As shown in the figure, fluid fills a container having several sections. At which of the indicated points is the pressure greatest?

The pressure is the same at each of the labeled poin

A push of magnitude P acts on a box of weight W as shown in the figure. The push is directed at an angle θ below the horizontal, and the box remains a rest. The box rests on a horizontal surface that has some friction with the box. The normal force on the box due to the floor is equal to:

W + P sin θ

An object is moving with constant non-zero acceleration in the +x direction. The velocity versus time graph of this object is...

a straight line making an angle with the time axis.

A car moving at a steady 10 m/s on a level highway encounters a depression that has a circular cross-section with a radius of 30 m. The car maintains its speed as it drives through the depression. What is the normal force exerted by the seat of the car on a 60 kg passenger when the car is at the bottom of the depression?

a=v^2/r = 10^2 / 30 = 3.333 F = 60*3.333 + 60*9.8 = 790 790 N

You are in a train traveling on a horizontal track and notice that a piece of luggage starts to slide directly toward the front of the train. From this observation, you can conclude that this train is...

accelerating backward.

A pilot drops a package from a plane flying horizontally at a constant speed. Neglecting air resistance, when the package hits the ground the horizontal location of the plane will...

be directly over the package.

Suppose a ball is thrown straight up and experiences no appreciable air resistance. What is its acceleration just before it reaches its highest point?

exactly g

In an inelastic collision involving an isolated system, the final total momentum is...

exactly the same as the initial momentum.

A person sits on a freely spinning lab stool that has no friction in its axle. The person is spun around by a friend. When this person extends her arms while spinning...

her moment of inertia increases and her angular speed decreases.

You have two identical eggs. You drop one egg onto the floor and notice that it comes to a stop abruptly. The other egg you drop from the same height onto a thick piece of foam rubber and notice that the stop is more gradual. In both cases, the egg does not bounce. In which case is the impulse greater? In which case is the average force greater?

impulse is the same in both cases, but average force is greater with floor

An air bubble underwater has the same pressure as that of the surrounding water. As the air bubble rises toward the surface (and its temperature remains constant), the volume of the air bubble...

increases

A person who normally weighs 700 N is riding in an elevator that is moving upward but slowing down at a steady rate. If this person is standing on a bathroom scale inside the elevator, what would the scale read?

less than 700 N

As shown in the figure, a 60 cm length of uniform wire, of mass 60 g, is bent into a right triangle. What are the x and y coordinates of the center of mass (or center of gravity) of this triangle?

m1 = 10g, m2 = 24g, m3=26g x=(0)(10)+(12)(24)+(12)(26)/60 y=(5)(10)+(0)(24)+(5)(26)/60 (10.0 cm, 3.0 cm)

A 100 kg person sits on a 5 kg bicycle. The total weight is supported equally by the two wheels of the bicycle. The tires are 2.0 cm wide and are inflated to a gauge pressure of 8.0 × 10^5 Pa. What length of each tire is in contact with the ground?

m=100+5=105 105*9.8/2=515 515/(8*10^5(2*10^-2)) = 3.2 3.2cm

A 1600 kg car is moving at 25 m/s around a horizontal unbanked curve that has a radius of 0.10 km. What is the magnitude of the friction force required to keep the car from sliding?

mv^2/r = 1600*25^2/100 10,000 N

A 10 kg piece of aluminum sits at the bottom of a lake, right next to a 10 kg piece of lead, which is much denser than aluminum. Which one has the greater buoyant force on it?

the aluminum

Two forces produce equal torques on a door about the door hinge. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force has a greater magnitude?

the first force (at the midpoint)

A waiter fills your water glass with ice water (containing many ice cubes) such that the liquid water is perfectly level with the rim of the glass. As the ice melts,...

the liquid-water level remains flush with the rim of the glass.

On an alien planet, an object moving at 4.0 m/s on the horizontal ground comes to rest after traveling a distance of 10 m. If the coefficient of kinetic friction between the object and the surface is 0.20, what is the value of g on that planet?

u*m*g*d=.5mv^2 .2*g*10=.5*4^2 4.0 m/s^2

Swimmers at a water park have a choice of two frictionless water slides, as shown in the figure. Although both slides drop over the same height h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the bottom of slide 1 compare with v2, the speed of a swimmer reaching the end of slide 2?

v1 = v2

An ideal gas occupies 6.00 × 102 cm3 at 20°C. At what temperature will it occupy 1.20 × 103 cm3 if the pressure is held constant?

v1/v2=t1/t2 600/1200=(273+20)/T2 T2=586=313C 313°C

A string is wound tightly around a fixed pulley having a radius of 5.0 cm. As the string is pulled, the pulley rotates without any slipping of the string. What is the angular speed of the pulley when the string is moving at 5.0 m/s?

v=5m/s r=5cm=.05m 5/.05=100 100 rad/s