# PHYSICS ( I am not very good at solving, I really need help. Please and thank you :) )  1. Explain each of the following statements, using Newton's first law to support them: a) You should hold on...

PHYSICS ( I am not very good at solving, I really need help. Please and thank you :) )

1. Explain each of the following statements, using Newton's first law to support them:

a) You should hold on to something when standing on a bus while it is moving.

b) An ice skater coasts across a rink with a constant velocity even when she isn't actively skating.

2. A skateboarder moving at 4.0 m/s [S] accelerates uniformly to 16.0 m/s [S] in 6.0 s. Find the average acceleration of the skateboarder.

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3. Complete each of the following problems by finding the missing information:

a) Find the mass of a cart that accelerates at 1.5 m/s2 [N] when a net force of 12.0 N [N] acts on it.``

b) A cyclist (total mass of 80kg, bike plus person) starts from rest and accelerates to a velocity of 12.0 m/s [E] in 4.0s. Find the net force acting on the cyclist and the bike.

sciftw | High School Teacher | (Level 1) Educator Emeritus

Posted on

1a. You are standing on a bus. It is moving at 20 mph. You are also moving at 20 mph relative to the street outside of the bus. Newton's first law says that you will continue to move at that speed and in that direction unless an unbalanced force is applied to you.  So when the bus driver slams on the brakes to avoid hitting a little lost kitten, you will be flung to the front of the bus because Newton's first law says that you will continue to move. So hold on to something in order to stop yourself .

1b. Technically that's not possible. Ice has low friction, but it HAS friction. You will be slowing down. But I get what the question is asking. Use Newton's first law again. The skater is moving at a constant velocity and the law says that will continue to happen unless an outside force changes that motion.

2. The formula for average acceleration is (final velocity - starting velocity )/ time to change velocities.  Plug in the numbers. (16-4)/6 = acceleration .  (12)/6 = acceleration.   2 m/s/s = acceleration.

3a. This question is using Newton's second law. The law states that force, mass, and acceleration are all related. For example, the acceleration of an object depends on the force applied and the mass of the object. The formula is A = F/M.   Rework the formula to solve for mass and it looks like this: M = F/A. Plug in your known values.  M = 12/1.5     You get a mass of 8 kg.

3b. The question is still making use of Newton's second law. Use the formula A = F/M and rework it to isolate force. That looks like F = M x A.   F = 80 x 12     F = 960 N