Question 26

Question

How many half-lives does it take a radioactive substance to decay until only one-eighth of the original substance remains?

a
eight
b
two
c
six
d
three
Question 27
The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

a
25 g
b
100 g
c
50 g
d
75 g
Question 28
Look at Zeke.

He’s riding his skateboard down a ramp. Assume that his acceleration is 0.8 m/s2. How much force does it take for him to accelerate at this rate? Zeke has a mass of 50 kg.

a
40 N
b
62.5 N
c
40 kg
d
50 N
Question 29
As you are walking, you foot gets caught on an uneven piece of sidewalk and you trip and fall. Which of the following explains what is happening using Newton's Laws?

a
The sidewalk pushed you, causing a rapid force that made you fall
b
The sidewalk provided a force to stop your foot, but the top of your body was still moving which is what causes you to tip over
c
Your foot hit the sidewalk and provided a force on it, so the sidewalk will provide another force back on your foot, equal in magnitude but opposite in direct
d
Your foot pushes the sidewalk with such force that it causes the next piece of sidewalk to be uprooted, which makes your next step miss your footing
Question 30
A block with a mass of 55 kg is pulled with a force of 220 N. Assuming a frictionless surface, what will be the acceleration of the block?

a
4.0 m/s2

b
22 m/s2

c
9.8 m/s2

d
0.25 m/s2

Question 31
Trial Force (N) Acceleration (m/s^2)
1 10 N 2.5
2 12 3
3 22 5.5
Students are running an experiment in which they are measuring the acceleration after applying forces to a cart. Using the data above, what is the mass of the cart?

a
2 kg
b
4 kg
c
6 kg
d
8 kg
Question 32
According to Newton's Third Law, if a sledgehammer hits a wall with a force of 1000 N, how much force does the wall hit the sledgehammer?

a
0 N
b
500 N
c
1000 N
d
- 1000 N
Question 33
Which of the following would be a situation with unbalanced forces?

a
Two people pulling on the same side of a wheelbarrow
b
A team of players in tug of war pulling on the rope, each team with equal numbers of people pulling with equal strength
c
Two people of opposite sides of a big tire. One pushes the tire and one pulls it with equal force
d
Two people not touching a crate that is sitting stationary
Question 34
Why is it generally easier to push a heavy object that is already moving instead of the same heavy object that is stationary

a
The force of gravity on the object is different if it is stationary or not.
b
The force of friction on the object is different if it is stationary or not
c
The force of the push on the object is different if it is stationary or not
d
The normal force on the object is different if it is stationary or not

Answer 1

Here are the answers to your questions:

Question 26: How many half-lives does it take a radioactive substance to decay until only one-eighth of the original substance remains?

• Answer: d - three (After 1 half-life, 1/2 remains; after 2 half-lives, 1/4 remains; after 3 half-lives, 1/8 remains.)

Question 27: The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

• Answer: a - 25 g (After 5 days: 50 g remains, after another 5 days: 25 g remains.)

Question 28: He’s riding his skateboard down a ramp. Assume that his acceleration is 0.8 m/s². How much force does it take for him to accelerate at this rate? Zeke has a mass of 50 kg.

• Answer: b - 40 N (Using F = ma, F = 50 kg * 0.8 m/s² = 40 N.)

Question 29: As you are walking, your foot gets caught on an uneven piece of sidewalk and you trip and fall. Which of the following explains what is happening using Newton's Laws?

• Answer: b - The sidewalk provided a force to stop your foot, but the top of your body was still moving which is what causes you to tip over.

Question 30: A block with a mass of 55 kg is pulled with a force of 220 N. Assuming a frictionless surface, what will be the acceleration of the block?

• Answer: a - 4.0 m/s² (Using F = ma, a = F/m = 220 N / 55 kg = 4 m/s².)

Question 31: Using the data above, what is the mass of the cart?

• Answer: b - 4 kg (From trial 1, using F = ma: 10 N = m * 2.5 m/s², m = 10 N / 2.5 m/s² = 4 kg.)

Question 32: According to Newton's Third Law, if a sledgehammer hits a wall with a force of 1000 N, how much force does the wall hit the sledgehammer?

• Answer: c - 1000 N (According to Newton’s Third Law, forces are equal and opposite.)

Question 33: Which of the following would be a situation with unbalanced forces?

• Answer: a - Two people pulling on the same side of a wheelbarrow (This would create an unbalanced force because both are pulling in the same direction.)

Question 34: Why is it generally easier to push a heavy object that is already moving instead of the same heavy object that is stationary?

• Answer: b - The force of friction on the object is different if it is stationary or not (Static friction is usually greater than kinetic friction, making it easier to push an object that is already in motion.)

Feel free to ask if you have any more questions!