# Lesson Worksheet: Distinguishing Weight from Other Forces Physics • 9th Grade

In this worksheet, we will practice distinguishing between the effects of the weight of an object and other forces that may be acting on it.

Q1:

A car has a mass of 460 kg. The weight of the car is evenly supported by its four identical wheels. What force does each wheel apply to the ground?

Q2:

An astronaut who has a mass of 80 kg is in a space station that orbits Earth in free fall. The astronaut is floating in a room of the space station, touching a wall that is perpendicular to Earth’s surface with her hand. She pushes against the wall with a force of 20 N. What is her acceleration perpendicular to the wall?

Q3:

A child who has a mass of 30 kg jumps into the air and lands on the ground. The child hits the ground at a speed of 1 m/s and comes to rest 0.1 s after landing.

What is the child’s weight?

What is the average force applied to the ground by the child’s feet during the landing?

Q4:

A climber is standing at the base of a cliff, holding onto a rope that is attached to the top of the cliff. The climber is pulling on the rope in order to pull himself off from the ground, but his feet stay in contact with the ground, just not supporting the climber’s full weight. The climber’s mass is 50 kg and the rope exerts an upward vertical force of 150 N on the climber. What is the force exerted on the ground beneath the climber due to his weight?

Q5:

A rock with a mass of 2.5 kg is thrown vertically upward by an applied force of 60 N.

What is the rock’s weight?

What is the net vertically upward force applied to the rock?

What is the rock’s rate of upward vertical acceleration just before it is released?

What is the rock’s rate of upward vertical acceleration just after it is released?

• A9.8 m/s2
• B35.5 m/s2
• C m/s2
• D14.2 m/s2
• E m/s2

Q6:

A swimmer in fresh water starts to slowly sink while not actively making an effort to stay afloat. The swimmer’s mass is 55 kg. When sinking, the swimmer accelerates downward at 0.3 m/s2.

What is the swimmer’s weight?

What is the vertical force acting on the swimmer from the water? Consider the swimmer’s weight to have a positive value.

Q7:

An athlete lands on a trampoline and stretches the trampoline mat to its maximum deformation by exerting a force on it, which includes her weight. Assume that the athlete’s weight acts on the trampoline as soon as her feet make contact with it and continues to do so while she remains in contact with the trampoline. The athlete comes to rest when the trampoline is fully deformed. The force of the athlete’s weight is shown in the graph in red, and the force due to the athlete’s deceleration is shown in blue. Which of the graphs (a), (b), (c), and (d) correctly shows the net force on the trampoline?

• A(b)
• B(c)
• C(a)
• D(d)

Q8:

A person with a mass of 60 kg is standing in an airplane cabin when the airplane starts to accelerate vertically downward at 9.8 m/s2. What is the weight of the person to the nearest newton?

Q9:

An athlete with a mass of 45 kg lands on a trampoline, as shown in the diagram. The athlete stretches the trampoline mat to its maximum deformation by exerting a total force of 900 N on it, which includes her weight. Assume that the athlete’s weight acts on the trampoline as soon as her feet make contact with it and continues to do so while she remains in contact with the trampoline. The athlete lands on the trampoline moving at 7.5 m/s and comes to rest when the trampoline is fully deformed.

How much does the athlete’s momentum change?

How much time does it take for the trampoline to be fully deformed? Answer to two decimal places.

Q10:

An astronaut is on the Moon, where the acceleration due to gravity is 1.6 m/s2. The astronaut is assembling a structure that will become a part of a moon base. One part of the structure is a pole that has a mass of 32 kg. The pole is suspended from a cable that holds it off the ground. When the pole is moved, the cable releases the pole. The astronaut pushes the pole horizontally, releasing it from the cable, and the pole accelerates horizontally at 2 m/s2 while the astronaut pushes it, as shown in the diagram. What force does the astronaut apply to the pole?