Question 1

A 92.5 kg stunt man stands on a piston that will launch him out of a vertical tube. The piston applies a constant force F to the man's feet. Starting from rest, the force is applied for 1.20 s, and during that time interval, the man attains a velocity of 25.5 m/s. What was the man's apparent weight during this time interval?
A) Unable to answer without knowing the value of F.
B) 3740 N
C) 1970 N
D) 2830 N
E) 2870 N

Accepted Answer

The apparent weight is the normal force exerted by the piston, which is the sum of the gravitational force and the force due to acceleration. Calculate acceleration using $ a = \frac{\Delta v}{\Delta t} = \frac{25.5 \, \text{m/s}}{1.20 \, \text{s}} = 21.25 \, \text{m/s}^2 $. The net force is $ F_{\text{net}} = ma = 92.5 \, \text{kg} \times 21.25 \, \text{m/s}^2 = 1965.625 \, \text{N} $. The gravitational force is $ F_g = mg = 92.5 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 906.5 \, \text{N} $. The apparent weight is $ F_{\text{apparent}} = F_{\text{net}} + F_g = 1965.625 \, \text{N} + 906.5 \, \text{N} = 2872.125 \, \text{N} \approx 2870 \, \text{N} $.

Question 2

A 92.5 kg stunt man stands on a piston that will launch him out of a vertical tube. The piston applies a constant force F to the man's feet. Starting from rest, the force is applied as the man moves vertically 3.25 m, and while the piston is pushing, the man attains a velocity of 25.5 m/s. What was the man's apparent weight during this time interval?
A) 9.3 kN
B) 18.5 kN
C) 19.4 kN
D) 10.2 kN

Accepted Answer

The answer of A 92.5 kg stunt man stands on...

Question 3

On the way to lower floors, an elevator begins its descent from rest with a constant acceleration, descending the first 5.0 m in 1.85 s. What is the apparent weight of a 75 kg man inside the accelerator during this time interval?
A) 0.74 kN
B) 0.52 kN
C) 0.11 kN
D) 1.0 kN

Accepted Answer

The apparent weight is the normal force, which is the actual weight minus the force due to acceleration. Using the equation $ s = ut + \frac{1}{2}at^2 $, we find acceleration $ a $. Then, apparent weight = $ mg - ma $.

Question 4

You are standing on a bathroom scale in an elevator that is not moving, and the scale reads 500 N. If the elevator were instead moving downward at a constant velocity of 4.50 m/s, what would the scale read?
A) 100 N
B) 450 N
C) 500 N
D) 750 N
E) 250 N

Accepted Answer

When the elevator is not moving, the scale reads the normal force exerted by the floor to support your weight, which is equal in magnitude and opposite in direction to your weight. Therefore, your weight is 500 N.

When the elevator is moving downward at a constant velocity, there is no net force acting on you, since the gravitational force and the normal force still cancel each other out. However, since you are now in a non-inertial reference frame (the accelerating elevator), you experience a fictitious force known as the "inertial force" or "pseudo force", which pushes you upward with a magnitude equal to your mass times the acceleration of the elevator (-4.50 m/s^2). This inertial force is what the scale reads as an additional force, so the scale reading will be the sum of the normal force and the inertial force.

Using Newton's second law (F = ma) and assuming your mass is 50 kg, we can calculate the magnitude of the inertial force:

F_inertial = m * a = 50 * (-4.50) = -225 N

Note that the negative sign indicates that the inertial force is directed upward (opposite to the direction of the elevator's motion).

Therefore, the scale reading when the elevator is moving downward at a constant velocity of 4.50 m/s is:

F_scale = F_weight + F_inertial = 500 + (-225) = 275 N

This is less than the scale reading when the elevator is not moving, but it is still larger than some of the answer choices, so the correct answer is C) 500 N.

Question 5

An object of mass m is hanging by a string from the roof of an elevator. The elevator is moving up at a constant speed. What is the tension in the string?
A) greater than mg
B) less than mg
C) equal to mg
D) depends on the speed of the elevator

Accepted Answer

When the elevator is moving up at a constant speed, the net force acting on the object is zero. Therefore, tension in the string is equal to the weight of the object (mg) in the opposite direction, according to Newton's second law.

Question 6

An object of mass m is hanging by a string from the roof of an elevator. The elevator is increasing its upward speed. What is the tension in the string?
A) greater than mg
B) less than mg
C) equal to mg
D) depends on the speed of the elevator

Accepted Answer

When the elevator is increasing its upward speed, it is accelerating upwards. This means the object experiences a greater force due to the combined effect of gravity and the upward acceleration of the elevator. Therefore, the tension in the string must be greater than mg to counteract these forces and hold the object in place.

Question 7

A skydiver has bailed out of his airplane at a height of 3000 m. The mass of the skydiver and his parachute is 80 kg. What is the drag (force of air resistance) on the system (man plus parachute) when he reaches terminal speed?
A) 120 N
B) 360 N
C) 784 N
D) 750 N

Accepted Answer

At terminal velocity, the force of air resistance (drag) is equal to the force of gravity acting on the skydiver and parachute system. The force of gravity can be found using the formula F = mg, where m is the mass and g is the acceleration due to gravity (9.8 m/s^2). 
Fg = (80 kg) * (9.8 m/s^2) = 784 N
Therefore, at terminal velocity, the drag on the system is also 784 N. Therefore, the correct choice is C, 784 N.

Question 8

A 35.0 kg girl swings on a swing set. At the bottom of the swing's path, she feels as though she weighs 435 N. What is the value of the tension in the swing's ropes at the bottom of the swing's path?
A) 92 N
B) 435 N
C) 343 N
D) 778 N

Accepted Answer

The answer of A 35.0 kg girl swings on a...

Question 9

An object of mass m is hanging by a string from the roof of an elevator. The elevator is moving downward and slowing down. What is the tension in the string?
A) greater than mg
B) less than mg
C) equal to mg
D) depends on the speed of the elevator

Accepted Answer

When the elevator is moving downward and slowing down, it is experiencing an upward acceleration. This means the tension in the string must be greater than the gravitational force (mg) to provide the net upward force required for the upward acceleration.

Question 10

Two masses are connected by a string which passes over a pulley with negligible mass and friction. One mass hangs vertically and one mass slides on a horizontal surface. The horizontal surface has a coefficient of kinetic friction of 0.200. The vertically hanging mass is 3.00 kg and the mass on the horizontal surface is 3.00 kg. The magnitude of the acceleration of the vertically hanging mass is (the initial velocity of the horizontal mass is to the right) A) 7.16 m/s². B) 5.88 m/s². C) 4.02 m/s². D) 3.53 m/s². E) 2.00 m/s².

Accepted Answer

The answer of Two masses are connected by a string...

Quiz 4: Force and Newtons Laws of Motion

On the way to lower floors, an elevator begins its descent from rest with a constant acceleration, descending the first 5.0 m in 1.85 s. What is the apparent weight of a 75 kg man inside the accelerator during this time interval?

You are standing on a bathroom scale in an elevator that is not moving, and the scale reads 500 N. If the elevator were instead moving downward at a constant velocity of 4.50 m/s, what would the scale read?

An object of mass m is hanging by a string from the roof of an elevator. The elevator is moving up at a constant speed. What is the tension in the string?

An object of mass m is hanging by a string from the roof of an elevator. The elevator is increasing its upward speed. What is the tension in the string?

A skydiver has bailed out of his airplane at a height of 3000 m. The mass of the skydiver and his parachute is 80 kg. What is the drag (force of air resistance) on the system (man plus parachute) when he reaches terminal speed?

A 35.0 kg girl swings on a swing set. At the bottom of the swing's path, she feels as though she weighs 435 N. What is the value of the tension in the swing's ropes at the bottom of the swing's path?

An object of mass m is hanging by a string from the roof of an elevator. The elevator is moving downward and slowing down. What is the tension in the string?