Question

forces quiz
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1. newtons major breakthrough on motion of everyday objects was...

a. objects that are moving keep moving forever unless something stops them.
b. objects that are moving tend to stop moving over time.
c. there are places on earth that are perfectly slippery where objects can keep moving forever.

1. if a kid jumps off a boat, the kid moves forward and the boat moves backward, but the kid moves faster than the boat. why?

a. because the force on the kid when they jump is bigger.
b. because the boat doesnt have any force on it.
c. because the force on the kid is the same as the force on the boat but the boat has a bigger mass.

1. if a kid is 40 kg, how hard (what force) would they need to jump to accelerate forward at 2 m/s²?

equations:
f = m × a
a = f_net/m

1. if your joking friend shoves you forward with a force of exactly 25 n, how much force does your body push back on their hands?

a. no force at all - 0 n
b. more than zero but less than 25 n
c. 25 n exactly

1. a person runs at constant speed as shown.

a. name each of the forces acting on the runner.

• force a
• force b
• force c
• force d

b. what is the net force on the runner?
force options:

1. gravity
2. normal
3. tension
4. friction
5. active
6. no force

Explanation:

Step1: Recall Newton's first - law for question 1

Newton's first law states that an object in motion will stay in motion with a constant velocity unless acted upon by an external force.
So the answer to question 1 is b.

Step2: Recall Newton's third - law and second - law for question 2

According to Newton's third - law, the force on the kid and the force on the boat are an action - reaction pair, so they are equal in magnitude. According to Newton's second - law $a=\frac{F}{m}$, with the same force, a larger mass results in a smaller acceleration. So the answer to question 2 is c.

Step3: Apply Newton's second - law for question 3

Given $m = 40\ kg$ and $a=2\ m/s^{2}$, using the formula $F = m\times a$.
$F=40\ kg\times2\ m/s^{2}=80\ N$

Step4: Recall Newton's third - law for question 4

Newton's third - law states that for every action, there is an equal and opposite reaction. So if a friend shoves you forward with a force of 25 N, your body pushes back on their hands with a force of 25 N exactly. The answer is c.

Step5: Analyze forces on a runner for question 5a

Force A is Gravity (pulling the runner downwards). Force B is Friction (pushing the runner forward as they push against the ground). Force C is No force (there is no force acting horizontally in the opposite direction of motion for a constant - speed runner assuming no air resistance etc.). Force D is Normal (pushing the runner upwards to balance gravity).
For question 5b, since the runner is running at a constant speed, according to Newton's first - law, the net force on the runner is 0 N.

Answer:

1. b. Objects that are moving keep moving forever unless something stops them.
2. c. Because the force on the kid is the same as the force on the boat but the boat has a bigger mass.
3. 80 N
4. c. 25 N exactly
5. a. Force A: Gravity; Force B: Friction; Force C: No force; Force D: Normal

b. 0 N