# Lesson Worksheet: Newton’s Second Law of Motion Physics • 9th Grade

In this worksheet, we will practice applying Newton’s second law of motion, F = ma, to find the acceleration caused by forces that act in various directions.

**Q1: **

A cell phone is at rest on a tabletop
and the phone’s owner flicks the phone with their fingers,
which applies a 0.01 N
force to the phone. The phone is accelerated at a
rate of 0.1 m/s^{2}
in the direction of the flick. What is the mass of the phone?

**Q2: **

A cup of mass 125 g is at rest on a desk when it is
accidentally knocked by a person’s arm. The cup accelerates in the
direction that it is pushed at a rate of 0.25 m/s^{2}. How much force is
applied by the arm that knocks the cup? Give your answer to two significant
figures.

**Q3: **

An object of mass 1.5 kg has a force of 4.5 N applied to it. At what rate does the force accelerate the object?

**Q4: **

An object with a mass of 5 kg accelerates left at 3 m/s^{2} while a force of 20 N is applied to it, acting to the right, and an unknown force is applied to it, acting to the left. What is the magnitude of the unknown force?

**Q5: **

An object of mass 7.5 kg has a force applied to it that pulls eastward with a magnitude of 50 N and another applied to it that pulls westward with a magnitude of 150 N. What is the westward acceleration of the object? Give your answer to one decimal place.

**Q6: **

How much force is applied to an object of mass 5 kg that is accelerated by that force at a rate of 2 m/s^{2}?

**Q7: **

An object accelerates at 4 m/s^{2} while a force of
20 N is applied to it. What is the mass of the object?

**Q8: **

A skateboarder of mass
50 kg
stands on a skateboard of mass
1.5 kg,
close to the wall of a building.
The skateboarder stands with one foot on the board and uses the other foot to push away from the wall.
The skateboard accelerates away from the wall at
4.66 m/s^{2}.
With how much force did the skateboarder push against the wall?
Give your answer to the nearest newton.

**Q9: **

A sheet of paper is at rest on a desk next to an open window. A short gust of wind blows in through the window and the sheet of paper is blown in the direction of the gust. The paper accelerates in the direction of the air flow at 0.33 m/s^{2}. The net force applied to the paper is 0.001 N to it. Find the mass of the paper to the nearest whole number of grams.

**Q10: **

A bolt that has a mass of 125 g is placed on a horizontally aligned crossbow and the crossbow’s string is tightened. The crossbow’s string is released when the crossbow trigger is pulled, and the recoiling string hits the bolt and applies a force of 45 N to it. The bolt flies away from the crossbow. What rate of acceleration does the bolt have in the direction of the push from the string?