Thought I'll get this thread started with some questions!
Simple questions on forces (VCE Physics Unit 2)
1. A rocket travels through empty space. Explain how the gases expelled by the rocket engine causes it to accelerate upwards. Make reference to one of Newtons Laws.
Answer
Whe the rocket expels the gases, the gases experience a force. As Newtons 3rd law states, this force will have an eqaul, but opposite reaction force. In this case, the gases exert a force on the rocket in the opposite direction, causing the rocket to accelerate.
2. Four forces are acting on a 1500kg boat being towed by a car. It is not moving upwards or downwards. (upwards = positive)
a) What is the gravitatational force acting on the boat?
b) What is the magnitude of the normal force acting on the boat?
c) Why is there a normal force?
d) The car pulling the boat acts with a force of 1300 N, while air resistance acts in the opposite direction with a force of 1000N. What is the net force?
e) Determine the boats acceleration.
Answers
a) 1500 x -9.8 = -14700N
b) 14700N
c) The boat exerts a contact force on the ground, as a result of gravity pulling it down. As a result of this contact force, reaction force is exerted on the ground, i.e. the normal force.
d) 1300 - 1000 = 300N
e) F = ma
300 = 1500a
a = 0.2m/s/s
3. What is the normal force?
Answer
The normal force is a reaction to a contact force.
So I hear that you are into Physics? 8)
Well I got some motion questions for you!!
A student drops a tennis ball from a 20m high building and 0.60s later, she throws a basketball with an initial velocity of 8m/s.
A) Calculate the time it takes for the tennis ball to reach the ground.
B) Draw a velocity-time graph to model this situation. (No need for numbers)
C) How long will it take for the basketball to pass the tennis ball?
Spoiler
a) s = ut + 1/2at^2
20 = 0 + 1/2 × 9.8 × t^2
t = 2s
b) (https://i.imgur.com/1426Qcj.png)
c) make s = ut + 1/2at^2 equal each other (simultaneous equation)
0 × t + 1/2 × 9.8 × t^2 = 8 × (t -0.6) + 1/2 × 9.8 × (t-0.6)^2
t = 1.43 seconds
A car has a max acceleration of 3.0m/s^2. What would the max acceleration be while towing a car twice its own mass?
Spoiler
1/3 × original acceleration (3) = 1m/s
Projectile Motion Question
(https://i.imgur.com/NrjrHMB.png)
a) What is the spear's location and velocity after 3.00 seconds? (Neglect the height of the person throwing the spear.)
b) How long will it take to hit the ground?
c) How far will it land from the ledge?
Spoiler
a)
Find horizontal first: 25 × cos(60) × 3 = 37.5m
Find Vertical: s = ut + 1/2at^2
s = 25 × sin(60) × 3 + 1/2 × -9.8 × 3^2
s = 20.9m
Coordinates are (37.5, 20.9)
Velocity:
v = u + at
v = 25 × sin(60) + -9.8 × 3
v = -7.75m/s
Add vector, Horizontal and Vectical with Pythagoras.
√((12.5)^2+(7.75)^2 )
= 14.71 m/s down and 31.8 degrees from horizontal. (Tan-1 (7.75/12.5))
b) s = ut + 1/2 at^2
50 = -21.65 × t + 1/2 × 9.8 × t^2
Use Quadratic Formula
t = 6.09s
c) 25 × cos(60) × 6.09 = 76.1m