Newton’s Laws
What does Newton’s First Law say about an object?
It will stay at rest or move at constant velocity.
Name three common forces that appear in free-body diagrams.
Gravity (Fg), Normal Force (Fn), Friction (Ff).
What is the acceleration due to gravity on Earth?
9.8 m/s²
What stays constant for an object in projectile motion?
Horizontal velocity
What does ΣF = 0 mean?
Forces are balanced; no acceleration.
A car continues moving at 20 m/s because the net force on it is zero. Which law explains this?
Newton’s 1st Law (Law of Inertia).
What does a free-body diagram show?
All forces acting on one object.
What’s the difference between mass and weight?
Mass = amount of matter; Weight = force of gravity (W = mg).
A ball is dropped. After 2 seconds, how fast is it moving (ignore air resistance)?
v = g×t = 9.8×2 = 19.6 m/s
A 12 kg cart is pulled by 36 N with 6 N friction. Find acceleration.
Fnet = 30 N → a = 30/12 = 2.5 m/s²
A 5 kg object accelerates at 3 m/s². What is the net force acting on it?
F = ma → 15 N
A box sits on a table at rest. What two forces act vertically, and how do they compare?
Fn upward = Fg downward; balanced.
Find the weight of a 60 kg person on Earth.
W=m×g
60kg×9.8m/s2=588N
A 20 N force acts at 60° above the horizontal. Find Fx and Fy.
Fx = 10 N, Fy = 17.3 N
A 2 kg block slides down a frictionless incline at 30°. Find Fgx.
Fgx = mg sinθ = 2×9.8×sin30 = 9.8 N
Explain how Newton’s Third Law applies when a swimmer pushes against the pool wall.
Swimmer pushes wall → wall pushes swimmer forward with equal and opposite force.
A 4 kg cart is pushed right with 12 N and friction is 3 N left. Find the net force.
9 N right
If Natalia (76 kg) goes to the Moon (1.62 m/s²), what’s her weight there?
W = 76 × 1.62 = 123 N
A satellite stays in orbit because it’s constantly “falling” toward Earth but never hits. What force acts as the centripetal force?
gravity
A 5 kg sled is pulled with 25 N at 40° (no friction). Find acceleration.
Fx = 25cos40 = 19.1 N → a = 19.1/5 = 3.8 m/s²
Two skaters push off each other with equal force. One skater has twice the mass. Who accelerates more and why?
The lighter skater; acceleration = F/m (smaller mass → greater acceleration).
A 5 kg box is pushed right with 20 N across a frictionless surface. Find its acceleration.
a = F/m = 20/5 = 4 m/s²
Two 70 kg people stand 1 meter apart. Calculate the gravitational force between them. (G = 6.67×10⁻¹¹)
F = 6.67×10⁻¹¹ × (70×70) / 1² = 3.3×10⁻⁷ N
A 10 kg box is pulled with 60 N at 35°. Find the horizontal acceleration (no friction).
Fx = 60cos35 = 49.2 N → a = 49.2/10 = 4.9 m/s²
A 4 kg block slides down a 25° incline with 5 N friction. Find acceleration.
Fgx = 4×9.8×sin25 = 16.6 N → Fnet = 16.6−5=11.6 N → a = 11.6/4=2.9 m/s²