physics midterm

The coordinate of an object is given as a function of time by x = 7t - 3t^2, where x is in meters and t is in seconds. Its average velocity over the interval from t = 0 to t = 2s is:

1 m/s

The number of significant figures in 150 is:

2

Let V = 2.00i + 6.00j − 3.00k. The magnitude of V is:

7.00

Why do raindrops fall with constant speed during the later stages of their descent?

Air resistance just balances the force of gravity

Which of the following is a correct statement of Newton's first law?

An object in motion will continue in motion at a constant velocity unless acted on by a net external force.

Vectors A and B lie in the xy plane. We can deduce that A = B if:

Ax = Bx and Ay = By

Which of the following is the correct combination of dimensions for energy?

ML^2/T^2

Which of the following bodies has the largest kinetic energy?

Mass 2M and speed 3V

There is no SI base unit for area because:

area can be expressed in terms of square meters

When the brakes of an automobile are applied, the road exerts the greatest retarding force:

just before the wheels start to slide

The result of (j x k) x (k x i) is :

k

The SI base unit for mass is:

kilogram

The work done by gravity during the descent of a projectile is:

positive

Two blocks (A and B) are in contact on a horizontal frictionless surface. A 36-N constant force is applied to A as shown. The magnitude of the force of A on B is:

30 N

The vectors a, b, and c are related by c = a - b. Which diagram below illustrates this relationship?

(not the diagrams that have obtuse angles, the one where tip of c is at tip of a)

Two forces, one with magnitude of 3 N and the other with magnitude of 5 N, are applied to an object. For which orientation of the forces shown in the diagrams is the magnitude of the acceleration of the object the least?

(the diagram with the two forces horizontal and in opposite directions)

A 5-kg projectile is fired over level ground with a velocity of 200 m/s at an angle of 25◦ above the horizontal. Just before it hits the ground its speed is 150 m/s. Over the entire trip the change in the thermal energy of the projectile and air is:

+44,000 J

A 4-kg cart starts up an incline with a speed of 3 m/s and comes to rest 2 m up the incline.The total work done on the cart is:

-18 J

A car starts from Hither, goes 50 km in a straight line to Yon, immediately turns around, and returns to Hither. The time for this round trip is 2 hours. The magnitude of the average velocity of the car for this round trip is:

0 km/h

A forward horizontal force of 12 N is used to pull a 240-N crate at constant velocity across a horizontal floor. The coefficient of friction is:

0.05

A block is placed on a rough wooden plane. It is found that when the plane is tilted 30◦ to the horizontal, the block will slide down at constant speed. The coefficient of kinetic friction of the block with the plane is:

0.577

The magnitude of the force required to cause a 0.04-kg object to move at 0.6 m/s in a circle of radius 1.0 m is:

1.4×10−2 N

The angle between A = -(25 m)ˆi + (45 m)ˆj and the positive x axis is:

119

A vector of magnitude 20 is added to a vector of magnitude 25. The magnitude of this sum can be:

12

A box with a weight of 50 N rests on a horizontal surface. A person pulls horizontally on it with a force of 15 N and it does not move. To start it moving, a second person pulls vertically upward on the box. If the coefficient of static friction is 4.0, what is the smallest vertical force for which the box moves?

12 N

A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30◦ with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate of 1.5 m/s^2, then the work done by the man is:

140 J

Let A = (2 m)i+ (6 m)j−(3 m)k and B = (4 m)i+ (2 m)j+ (1 m)k. Then A dot B equals:

17

A motionless 400-N steel ball is suspended by a light rope from the ceiling. The tension in the rope is:

400 N

The block shown moves with constant velocity on a horizontal surface. Two of the forces on it are shown. A frictional force exerted by the surface is the only other horizontal force on the block. The frictional force is:

2 N, leftward

A constant force of 8.0 N is exerted for 4.0 s on a 16-kg object initially at rest. The total change in speed of this object after 4.0 s will be:

2.0 m/s

A right circular cylinder with a radius of 0.023 m and a height of 1.40 m has a volume (pi r^2h) of:

2.3x10^-3m^3

A sledge (including load) weighs 5000 N. It is pulled on level snow by a dog team exerting a horizontal force on it. The coefficient of kinetic friction between sledge and snow is 0.05. How much work is done by the dog team pulling the sledge 1000 m at constant speed?

2.5×10^5 J

A particle moves 5 m in the positive x direction while being acted upon by a constant force F = (4 N)i + (2 N)j −(4 N)k. The work done on the particle by this force is:

20 J

A giant wheel, having a diameter of 40 m, is fitted with a cage and platform on which a man of mass m stands. The wheel is rotated in a vertical plane at such a speed that the force exerted by the man on the platform is equal to his weight when the cage is at X, as shown. The net force on the man at point X is:

2mg, down

The number of significant figures in 0.00150 is:

3

Which of the following has three significant figures?

3050cm

A 6.0-kg block is released from rest 80 m above the ground. Neither external, nor friction forces act on it. When it has fallen 60 m from its original position, its kinetic energy is approximately:

3500 J

The long pendulum shown is drawn aside until the ball has risen 0.50 m. It is then given an initial speed of 3.0 m/s. The speed of the ball at its lowest position is:

4.3 m/s

If A = (6 m)ˆi −(8 m)ˆj then 4A has magnitude:

40m

A 8000-N car is traveling at 12 m/s along a horizontal road when the brakes are applied. The car skids to a stop in 4.0 s. How much kinetic energy does the car lose in this time?

5.9×10^4 J

An ideal spring, with a pointer attached to its end, hangs next to a scale. With a 100-N weight attached, the pointer indicates "40" on the scale as shown. Using a 200-N weight instead results in "60" on the scale. Using an unknown weight X instead results in "30" on the scale. The weight of X is:

50 N

A car starts from Hither, goes 50 km in a straight line to Yon, immediately turns around, and returns to Hither. The time for this round trip is 2 hours. The average speed of the car for this round trip is:

50 km/h

A 50-N force is the only force on a 2-kg object that starts from rest. At the moment the crate has moved a distance of 2 m the instantaneous power is:

500 W

What is the result of (0.410 + 0.021) x (2.20 x 10^3)?

948

Which of the five graphs correctly shows the potential energy of a spring as a function of its elongation x?

III (parabola opening up)

The first graph shows the potential energy U(x) for a particle moving on the x axis. Which of the other five graphs correctly gives the force F exerted on the particle?

III (the negative line going from quadrant II to quadrant IV)

Objects A and B interact with each other via both conservative and nonconservative forces. There are no external forces. Let KA and KB be the kinetic energies, U be the potential energy, and Eth be the thermal energy. If no external agent does work on the objects then:

KA + KB +U +Eth is conserved

A boy pulls a wooden box along a rough horizontal floor at constant speed by means of a force P as shown. In the diagram f is the magnitude of the force of friction, N is the magnitude of the normal force, and Fg is the magnitude of the force of gravity. Which of the following must be true?

P = f and N = Fg

A brick slides at constant velocity on a horizontal surface. Which of the following will increase the frictional force on it?

Putting a second brick on top

A small object of mass m starts from rest at the position shown and slides along the frictionless loop-the-loop track of radius R. What is the smallest value of y such that the object will slide without losing contact with the looped portion of the track?

R/2

Four students measure the mass of an object, each using a different scale. They record their results as:...Which student used a scale with graduations of 1g?

Student D 49.2

Suppose A = BC, where A has the dimension L/M and C has the dimension L/T. Then B has the dimension:

T/M

Which of the following is true, according to Newton's second law?

The acceleration of an object is proportional to the net force on it and inversely proportional to its mass.

When a certain rubber band is stretched a distance x, it exerts a restoring force of magnitude F = ax + bx^2, where a and b are constants. The work done in stretching this rubber band from x = 0 to x = L is:

aL^2/2 + bL^3/3

No kinetic energy is possessed by:

an elevator standing at the fifth floor

Let S = (1 m)i + (2 m)j + (2 m)k and T = (3 m)i + (4 m)k. The angle between these two vectors is given by:

cos−1(11/15)

The vector −A is:

in the direction opposite to A

A heavy wooden block is dragged by force, F, along a rough steel plate, as shown below for two cases. The magnitude of the applied force, F, is the same for both cases. The normal force in (ii), as compared to the normal force in (i) is:

less

The SI base units have the dimensions of:

mass, length, time

The potential energy of a body of mass m is given by U = −mgx+ 1/2kx^2. The corresponding force is:

mg - kx

Acceleration is always in the direction

of the net force

An elevator is rising at constant speed. Consider the following statements:

only I, II, and IV are true

A particle moves from point x1 to point x2. Its displacement is given by:

x2 - x1

A Newton is the force:

that gives a 1 kg body an acceleration of 1 m/s^2

In uniform circular motion,

the acceleration and the velocity are always perpendicular

A ball of mass m is thrown downward from the edge of a cliff with an initial speed that is three times the terminal speed. Initially the drag force on it is:

upward and greater than mg

Mass differs from weight in that:

weight is a force and mass is not

A golf ball is struck by a golf club and falls on a green eight feet above the tee. The potential energy of the Earth-ball system is greatest:

when the ball reaches the highest point in its flight

A block is attached to the end of an ideal spring and moved from coordinate xi to coordinate xf. The relaxed position is at x = 0. The work done by spring is positive if:

xi = −4 cm and xf = −2 cm

A particle moves along the x axis from xi to xf. Of the following values of the initial and final coordinates, which results in a negative displacement?

xi = −4 m, xf = −8 m