Question 1

A net force of 100.0 N is applied to a certain object. As a result, the object accelerates with an acceleration of G)What is the mass of the object?

Accepted Answer

B

Question 2

The mass of a human leg below the knee is 0.60 of the mass above the knee, and its centre of mass is located at 0.3 of the length of the lower leg from the knee joint. When the leg is bent from straight to a right angle at the knee, by what amount does the centre of mass of the leg shift? Express your answer in terms of the length of the leg below the knee.

Accepted Answer

When the leg is bent, the center of mass of the lower leg moves from 0.3 of its length to directly below the knee. The shift in the center of mass is calculated by considering the weighted average of the two segments. The shift is 0.11 times the length of the lower leg.

Question 3

Two cars of equal mass, one travelling north and the other east, collide at the same speed at right angles to each other. Assuming the collision is inelastic, what is the velocity following the collision?

Accepted Answer

C

Question 4

There are 15 billiard balls in a rack. The rack is removed. The balls are in triangular formation with the tip toward the cue ball. The cue ball is shot into the ball on the tip of the triangle. Assuming all balls have the same mass, in which direction does the net velocity vector of the set of balls point soon after the cue ball strikes them?

Accepted Answer

The answer of There are 15 billiard balls in a...

Question 5

A source of alpha particles bombards a target of gold. A small fraction of alpha particles return in a direction opposite to that of the ingoing source particles. Which of the following statements accurately describes the cause of this phenomenon?

Accepted Answer

The phenomenon described is due to the electrostatic repulsion between the positively charged alpha particles and the positively charged gold nuclei when they meet head-on. This is a classic demonstration of Rutherford's gold foil experiment, which helped establish the nuclear model of the atom.

Question 6

A railway boxcar is moving toward a stationary boxcar on a rail with negligible friction. The stationary boxcar is twice the mass of the moving one. On collision, the boxcars couple to each other. After the collision, what is the velocity of the more massive boxcar? Express your answer as a fraction of the velocity of the less massive boxcar before the collision.

Accepted Answer

Using conservation of momentum, the final velocity of the coupled boxcars is one-third of the initial velocity of the moving boxcar.

Question 7

3. A 1 kg ball travels at velocity v = +5 m/s horizontally to the right, hits a vertical wall, and bounces back to the left with velocity v = -5 m/s. What is the impulse exerted on the ball?

Accepted Answer

The answer of 3. A 1 kg ball travels at...

Question 8

Three railway cars of equal mass are on the same (frictionless) track. The one on the left is moving with velocity V toward the other two which are stationary. As the cars undergo successive collisions, they couple and move together. What is the velocity of the final configuration of the three coupled cars?

Accepted Answer

The velocity of the final configuration of the three coupled cars is V/3 due to the conservation of momentum. Since all cars have equal mass and the system is closed (no external forces), the total momentum before and after the collisions must be the same. Initially, only one car has momentum (mass * velocity), and after all collisions, the total mass is three times larger while the momentum remains constant, leading to a final velocity of V/3.

Question 9

Assuming a classical picture of the atom, an electron is captured into a circular orbit about a spherically shaped, singly charged ion, thus neutralizing it. In the frame of reference of the ion, the neutral atom acquires a component of velocity that is

Accepted Answer

In the frame of reference of the ion, when an electron is captured into orbit around it, the system's center of mass must remain stationary if no external forces are acting on it. Since the electron has momentum in a certain direction at the moment of capture, to conserve momentum, the newly formed neutral atom (ion + electron) must have a component of velocity in the same direction as the incoming electron. This ensures the total momentum of the system before and after the capture remains constant.

Question 10

A fireman is sliding down a fire pole. As he speeds up, he tightens his grip on the pole, thus increasing the vertical frictional force that the pole exerts on the fireman. When this force equals the weight of the fireman, which of the following happens?

Accepted Answer

When the vertical frictional force equals the weight of the fireman, the net force acting on the fireman becomes zero. According to Newton's second law, when the net force is zero, the acceleration is also zero, meaning the fireman will continue moving at whatever speed he has at that moment, which is a constant speed.

Question 11

An object is moving with constant velocity. Which of these statements accurately describes this?

Accepted Answer

When an object moves with constant velocity, it means there is no acceleration. According to Newton's first law of motion, this implies that the net force acting on the object is zero. Forces may be present, but they balance each other out.

Question 12

A squid ejects a bolus of water in order to escape a predator. The squid has a mass of 0.4 kg with its water cavity empty, and needs to escape with a speed of at least 0.8 m/s. If the ejected water has a mass of 0.1 kg, how fast must it be ejected in order for the squid to escape?

Accepted Answer

Using conservation of momentum, the momentum of the squid and water system before and after ejection must be equal. The initial momentum is zero, so 0.4 kg * 0.8 m/s = 0.1 kg * v. Solving for v gives v = 3.2 m/s.

Question 13

A car of mass m travelling at 40.0 km/hr collides head-on with a stationary car of equal mass, and stays attached until the pair come to a stop. The car in motion does NOT apply the brakes, whereas the stationary car has a braking force of 0.2mg. At what distance from the collision site does the pair of cars come to rest?

Accepted Answer

The answer of A car of mass m travelling at...

Question 14

You are falling from your tree house. Which of these actions could slow the fall? Ignore the effects of air resistance.

Accepted Answer

Ignoring air resistance, no internal forces or movements (such as rotating, stretching upwards, or sideways) can alter the motion of the center of mass of a system. According to the conservation of momentum, the center of mass of a system will continue to move in the same way unless acted upon by an external force.

Question 15

A ball rolls in a straight line without friction across the horizontal floor of a descending elevator. As the elevator comes to a stop, which of the following happens to the ball?

Accepted Answer

The ball continues its horizontal motion unchanged because there is no friction acting on it, and the horizontal motion is independent of the vertical motion of the elevator.

Question 16

A spaceship and docking module travelling in parallel come alongside each other at the same speed. The module fires a small rocket at a right angle to its motion to bring the module into contact with the spaceship for docking. On docking, which one of these effects does this have on the motion of the combined craft?

Accepted Answer

When the module fires a rocket at a right angle to its motion to dock with the spaceship, it imparts a small velocity component in that direction to the combined system, thus they acquire a small component of velocity perpendicular to the original motion.

Question 17

A 1000 kg car moving at 20 km/hr collides inelastically and head-on with a 10000 kg truck moving at 2 km/hr. Which one of these statements correctly describes the motion of the two vehicles after the collision?

Accepted Answer

The answer of A 1000 kg car moving at 20...

Question 18

A fish swimming with speed of 1.00 m/s is chasing its prey of 0.100 of its mass. It captures its prey when their relative velocity is 0.10 m/s. If the fish were to capture its prey when their relative velocity was 0.20 m/s, what would be the velocity of the fish in the second case relative to the first case?

Accepted Answer

The answer of A fish swimming with speed of 1.00...

Question 19

The thigh has a mass of 21.5 units, and its centre of mass is 9.6 units from the hip joint. The corresponding mass and length units for the knee are 9.6, 33.9; and for the ankle, 3.4, 50.3. Where is the centre of mass of the outstretched leg located relative to the hip bone?

Accepted Answer

The answer of The thigh has a mass of 21.5...

Question 20

A pair of railway boxcars are moving toward each other on a rail with negligible friction. One boxcar is twice the mass of the other. On collision, the boxcars couple to each other. In order for the coupled pair to have zero velocity (relative to a bystander next to the track) after the collision, what is the ratio of velocities of the more massive to the less massive boxcar before the collision?

Accepted Answer

For the total momentum of the system to be zero (which is necessary for the coupled boxcars to have zero velocity), the momentum of the two boxcars before the collision must cancel each other out. Since momentum is the product of mass and velocity, and one boxcar has twice the mass of the other, its velocity must be half but in the opposite direction (negative sign) for the momenta to cancel out. Hence, the ratio of the velocities is -1/2.

Quiz 5: Centre of Mass and Linear Momentum

A net force of 100.0 N is applied to a certain object. As a result, the object accelerates with an acceleration of G) What is the mass of the object?