Q: A 65 kg person stands in an elevator that accelerates upward at $$2 \ \mathrm{m/s^2$}. $$What is the apparent weight of the person?

$$F_{\text{apparent}} = m(g + a) = 65 \times (9.8 + 2) = 754 \ \mathrm{N}$$

Q: A 400 g ball moves horizontally with a velocity $$v_x = \frac{15}{2} \ \mathrm{m/s}$$ for $$t \u003e 0 \ \mathrm{s}. $$What is the net force on the ball at $$t = 2 \ \mathrm{s}$$?

$$F_{\text{net}} = 0 \ \mathrm{N}$$

Q: A person stands in an elevator moving downward at a constant speed. What is the person's apparent weight?

$$F_{\text{apparent}} = m \times g$$

Q: A car accelerates from rest at $$2 \ \mathrm{m/s^2$}$$ for 5 seconds. What is its final velocity?

$$v = v_0$ + at = 0 + 2 \times 5 = 10 \ \mathrm{m/s}$$

Question 1

A 65 kg person stands in an elevator that accelerates upward at $$2 \ \mathrm{m/s^2$}. $$What is the apparent weight of the person?

Accepted Answer

$$F_{	ext{apparent}} = m(g + a) = 65 	imes (9.8 + 2) = 754 \ \mathrm{N}$$

Question 2

A 400 g ball moves horizontally with a velocity $$v_x = \frac{15}{2} \ \mathrm{m/s}$$ for $$t \u003e 0 \ \mathrm{s}. $$What is the net force on the ball at $$t = 2 \ \mathrm{s}$$?

Accepted Answer

$$F_{	ext{net}} = 0 \ \mathrm{N}$$

Question 3

During a drag race burnout, the car's tire spins clockwise while the brakes are applied and the car is held in place. Which of the following best describes the direction of the friction force acting on the tire?

Accepted Answer

The friction force acts backward, opposite to the direction the car would move.

Question 4

A puck slides across ice at a constant speed. What is the reaction force to the puck's weight?

Accepted Answer

The normal force exerted by the ice on the puck.

Question 5

A mysterious force knocks the Moon out of orbit and sends it falling toward Earth. Which statement is true about the Moon's motion (neglecting air resistance)?

Accepted Answer

The Moon is in free fall in Earth's gravity.

Question 6

You are trying to push a heavy crate across the floor, but it is not moving. What is the reaction force to the force of your hands pushing against the crate?

Accepted Answer

The force of the crate pushing back against your hands.

Question 7

A 100 kg block is released from rest and falls 1.0 m in 3.0 s, connected by a pulley to a block of mass $$m. $$What is the mass $$m of $$the block on the left? (Assume negligible friction and pulley mass.)

Accepted Answer

$$m = 98 \ \mathrm{kg}$$

Question 8

A 300 g sphere revolves in a horizontal circle at a constant tangential speed of $$7.5 \ \mathrm{m/s}$$, suspended by two wires as shown. What is the tension in the upper wire?

Accepted Answer

$$T = 4.5 \ \mathrm{N}$$

Question 9

Which of the following graphs best represents the velocity vs. time for a car that moves to the right, speeds up, and then slows down?

Accepted Answer

A graph that starts at zero, increases to a maximum, then decreases back to zero.

Question 10

A person stands in an elevator moving downward at a constant speed. What is the person's apparent weight?

Accepted Answer

$$F_{	ext{apparent}} = m 	imes g$$

Question 11

A ball is thrown horizontally from a height of 10 m with a speed of $$5 \ \mathrm{m/s}. $$How long does it take to hit the ground? (Neglect air resistance.)

Accepted Answer

$$t = \sqrt{\frac{2h}{g}} = \sqrt{\frac{20}{9.8}} \approx 1.43 \ \mathrm{s}$$

Question 12

A car accelerates from rest at $$2 \ \mathrm{m/s^2$}$$ for 5 seconds. What is its final velocity?

Accepted Answer

$$v = v_0$ + at = 0 + 2 	imes 5 = 10 \ \mathrm{m/s}$$

Question 13

A block slides down a frictionless incline of height $$h. $$What is its speed at the bottom?

Accepted Answer

$$v = \sqrt{2gh}$$

Question 14

A 2 kg object moves in a circle of radius 0.5 m at a speed of $$4 \ \mathrm{m/s}. $$What is the centripetal force acting on it?

Accepted Answer

$$F_c = \frac{mv^2$}{r} = \frac{2 	imes 16}{0.5} = 64 \ \mathrm{N}$$

Question 15

A car moves to the left at a constant speed. Which velocity vs. time graph best represents this motion?

Accepted Answer

A horizontal line below zero on the velocity axis.

Question 16

A block of mass $$m is $$suspended by a rope. What is the tension in the rope if the block is at rest?

Accepted Answer

$$T = mg$$

Question 17

A car moves to the right and is slowing down at a steady rate. Which velocity vs. time graph best represents this motion?

Accepted Answer

A line that starts above zero and slopes downward toward zero.

Question 18

A 5 kg object is dropped from rest. What is its velocity after 3 seconds? (Neglect air resistance.)

Accepted Answer

$$v = v_0$ + at = 0 + 9.8 	imes 3 = 29.4 \ \mathrm{m/s}$$

Question 19

A car moves to the right at a steady rate. Which velocity vs. time graph best represents this motion?

Accepted Answer

A horizontal line above zero on the velocity axis.

Fundamental Mechanics Concepts and Problem-Solving for PHYS 101

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