Q: A 60 kg passenger in a car experiences a horizontal force of $$4.00 \times 10^2$ N during a crash. What is the acceleration experienced by the passenger?

$$a = \frac{F}{m} = \frac{4.00 \times 10^2$}{60} = 6.67\ \mathrm{m/s^2$}$$

Q: A 100 kg block hangs from a rope. What is the tension in the rope if the block is stationary?

$$T = mg = 100 \times 9.8 = 980\ \mathrm{N}$$

Q: A 20 kg sled slides at 4.5 m/s onto a patch of snow with a friction force of 12 N. How far does it slide before coming to rest?

$$d = \frac{mv^2$}{2f} = \frac{20 \times (4.5)^2$}{2 \times 12} = 16.9\ \mathrm{m}$$

Question 1

A car crashes into a wall and comes to a sudden stop, but the crash dummy inside continues moving forward until it hits the dashboard. Which law of motion best explains why the dummy keeps moving?

Accepted Answer

Newton's first law: An object in motion remains in motion unless acted on by a net force.

Question 2

A 60 kg passenger in a car experiences a horizontal force of $$4.00 	imes 10^2$ N during a crash. What is the acceleration experienced by the passenger?

Accepted Answer

$$a = \frac{F}{m} = \frac{4.00 	imes 10^2$}{60} = 6.67\ \mathrm{m/s^2$}$$

Question 3

Which of the following is a long-range force?

Accepted Answer

Weight (gravitational force)

Question 4

A ball is rolling on a flat surface and comes to a stop due to friction. Which statement best describes the role of friction in this scenario?

Accepted Answer

Friction acts opposite to the direction of motion, causing the ball to decelerate.

Question 5

A 100 kg block hangs from a rope. What is the tension in the rope if the block is stationary?

Accepted Answer

$$T = mg = 100 	imes 9.8 = 980\ \mathrm{N}$$

Question 6

A car is being towed at a constant speed by a rope at a 20° angle above the horizontal. The friction force opposing the motion is 320 N. What is the horizontal component of the tension in the rope?

Accepted Answer

$$T_x = 320\ \mathrm{N}$$

Question 7

A 20 kg sled slides at 4.5 m/s onto a patch of snow with a friction force of 12 N. How far does it slide before coming to rest?

Accepted Answer

$$d = \frac{mv^2$}{2f} = \frac{20 	imes (4.5)^2$}{2 	imes 12} = 16.9\ \mathrm{m}$$

Question 8

A ball is tossed straight up. Just after it leaves the hand (ignore air resistance), what forces act on it?

Accepted Answer

Only the weight of the ball acting downward.

Question 9

A steel beam hangs from a cable as a crane lifts the beam. What forces act on the beam?

Accepted Answer

Gravity and tension in the cable.

Question 10

A ball rolls off a horizontal ramp and moves through the air (ignore air resistance). What force(s) act on the ball just after it leaves the ramp?

Accepted Answer

The weight of the ball acting vertically down.

Question 11

A car with mass $$m is $$being towed and accelerates from rest to velocity $$v in $$time $$t. $$The net force on the car is $$F. $$Which equation correctly relates these quantities according to Newton’s second law?

Accepted Answer

$$F = m a = m \frac{v}{t}$$

Question 12

A 40-car train travels at 40 mph on a straight track, while a skier speeds up as she skis downhill. On which is the net force greater?

Accepted Answer

The skier

Question 13

An object on a rope is lowered at a steadily decreasing speed. Which is true?

Accepted Answer

The rope tension is greater than the object’s weight.

Question 14

A block is at rest on a frictionless surface, held by a string at an angle. What must be true for the block to remain at rest?

Accepted Answer

The net force on the block must be zero.

Question 15

A rocket launches vertically. Which force is responsible for its upward acceleration?

Accepted Answer

Thrust from the expulsion of exhaust gases.

Question 16

A person pushes backward on the ground while walking. According to Newton’s third law, what is the reaction force?

Accepted Answer

The ground pushes forward on the person.

Question 17

A 51,000 kg airplane accelerates from rest to 70 m/s over a distance of 940 m. What is the net force required for this acceleration?

Accepted Answer

$$F = m a = 51,000 	imes \frac{(70)^2$}{2 	imes 940} = 134,000\ \mathrm{N}$$

Question 18

A compressed spring exerts a force on a box. What type of force is this?

Accepted Answer

Contact force

Question 19

A box is pulled by two ropes at different angles. How do you find the net force acting on the box?

Accepted Answer

By taking the vector sum of the two tension forces.

Forces and Newton’s Laws of Motion: Structured Study Notes

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