Question 1

A 1.5 kg crate falls from a height of 2.0 m onto an industrial spring scale with a spring constant of 1.5 *105 N/m.At its greatest compression the reading on the scale is:

Accepted Answer

A) 15 N 
B) 29 N 
C) 1.5 *103 N 
D) 2.1 * 103 N 
E) 3.0 * 103 N

Question 2

The mechanical advantage of any machine is:

Accepted Answer

A) the efficiency of the machine 
B) the work done by the machine 
C) the ratio of the work done by the machine to the work expended on it 
D) the ratio of the force exerted by the machine to the force applied to it 
E) the ratio of the force applied to the machine to the force exerted by it

Question 3

A particle starts from rest at time t = 0 and moves along the x axis.If the net force on it is proportional to t, its kinetic energy is proportional to:

Accepted Answer

A) t 
B) t2 
C) t4 
D) 1/t2 
E) none of the above

Question 4

In the plot shown of force vs.distance, approximately how much work is done in moving an object from x = 5 m to x = 15 m?

Accepted Answer

A) 10 J 
B) 55 J 
C) 125 J 
D) 275 J 
E) cannot be calculated without knowing the mass of the object

Question 5

Three identical springs (X, Y, Z)are arranged as shown.When a 4.0-kg mass is hung on X, the mass descends 3.0 cm.When a 6.0-kg mass is hung on Y, the mass descends:

Accepted Answer

A) 2.0 cm 
B) 4.0 cm 
C) 4.5 cm 
D) 6.0 cm 
E) 9.0 cm

Question 6

Two objects with masses, m1 and m2, have the same kinetic energy and are both moving to the right.The same constant force  is applied to the left to both masses.If m1 = 4m2, the ratio of the stopping distance of m1 to that of m2 is:

Accepted Answer

A) 1:4 
B) 4:1 
C) 1:2 
D) 2:1 
E) 1:1

Question 7

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.The force he exerts is parallel to the slope.If the speed of the crate is constant, then the work done by the man is:

Accepted Answer

A) -200 J 
B) 61 J 
C) 140 J 
D) 200 J 
E) 260 J

Question 8

Which of the following groups does NOT contain a scalar quantity?

Accepted Answer

A) velocity, force, energy 
B) displacement, acceleration, force 
C) acceleration, speed, energy 
D) energy, force, distance 
E) energy, weight, time

Question 9

Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope.The coefficient of kinetic friction is 0.05.How much work is done by the campers in pulling the equipment 1000 m if its speed is increasing at the constant rate of 0.20 m/s2?

Accepted Answer

A) -1.2* 106 J 
B) 1.2 *105 J 
C) 3.0 * 105 J 
D) 4.2 *105 J 
E) 4.1 * 106 J

Question 10

A Boston Red Sox baseball player catches a ball of mass m that is moving toward him with speed v.While bringing the ball to rest, his hand moves back a distance d.Assuming constant deceleration, the horizontal force exerted on the ball by his hand is:

Accepted Answer

A) mv/d 
B) mvd 
C) mv2/d 
D) 2mv/d 
E) mv2/(2d)

Question 11

An object moves in a circle at constant speed.The work done by the centripetal force is zero because:

Accepted Answer

A) the displacement for each revolution is zero 
B) the average force for each revolution is zero 
C) there is no friction 
D) the magnitude of the acceleration is zero 
E) the centripetal force is perpendicular to the velocity

Question 12

A baseball is hit high into the upper bleachers of left field.Over its entire flight the work done by gravity and the work done by air resistance, respectively, are:

Accepted Answer

A) positive; positive 
B) positive; negative 
C) negative; positive 
D) negative; negative 
E) unknown since vital information is lacking

Question 13

A spring of spring constant k is attached to a block of mass m.The spring moves the block through a displacement x.How can you calculate how much work the spring does on the block?

Accepted Answer

A) Multiply the spring force, kx, by the distance x. 
B) Multiply the spring force, ½ kx2, by the distance x. 
C) Integrate the spring force, kx, over the distance x. 
D) Integrate the spring force, ½ kx2, over the time it takes the block to move. 
E) You cannot calculate this without knowing the acceleration of the block.

Question 14

A particle moving along the x axis is acted upon by a single force F = F0e-kx, where F0 and k are constants.The particle is released from rest at x = 0.It will attain a maximum kinetic energy of:

Accepted Answer

A) F0/k 
B) F0/ek 
C) kF0 
D) 1/2(kF0)2 
E) kekF0

Question 15

Which of the following bodies has the largest kinetic energy?

Accepted Answer

A) Mass 3M and speed V 
B) Mass 3M and speed 2V 
C) Mass 2M and speed 3V 
D) Mass M and speed 4V 
E) All four of the above have the same kinetic energy

Question 16

When a certain rubber band is stretched a distance x, it exerts a restoring force of magnitude F = Ax, where A is a constant.The work done by a person in stretching this rubber band from x = 0 to x = L is:

Accepted Answer

A) AL2 
B) AL 
C) A + 2L2 
D) A/L 
E) AL2/2

Question 17

An 80-N crate slides with constant speed a distance of 5.0 m downward along a rough slope that makes an angle of 30° with the horizontal.The work done by the force of gravity is:

Accepted Answer

A) -400 J 
B) -200 J 
C) -69 J 
D) 200 J 
E) 400 J

Question 18

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

Accepted Answer

A) MLT 
B) LT2 /M 
C) ML2/T2 
D) M2L3T 
E) ML/T2

Question 19

A woman lifts a barbell 2.0 m in 5.0 s.If she lifts it the same distance in 10 s, the work done by her is:

Accepted Answer

A) four times as great 
B) two times as great 
C) the same 
D) half as great 
E) one-fourth as great

Question 20

A boy holds a 40-N weight at arm's length for 10 s.His arm is 1.5 m above the ground.The work done by the force of the boy on the weight while he is holding it is:

Accepted Answer

A) 0 J 
B) 6.1 J 
C) 40 J 
D) 60 J 
E) 90 J

Exam 7: Kinetic Energy and Work

A 1.5 kg crate falls from a height of 2.0 m onto an industrial spring scale with a spring constant of 1.5 *10⁵ N/m.At its greatest compression the reading on the scale is: