# Practice Problems

Solve the following problems. Show your work with your answers.

EQUATIONS:

v = d/t        a = v/t           Δv = vf – vi             p = m*v         F = m*a            g = 9.8 m/s2        Weight=m*g

CALCULATE THE FOLLOWING – SHOW YOUR WORK!!

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1. A motorcycle went from 0 m/s to 35 m/s in 5.1 s. What is the motorcycle’s acceleration?
2. A race car was clock going 52 m/s. At another point, 5 s later, it was clocked going 155 m/s. What was the car’s acceleration?
3. Calculate the speed of a bee flying 160 m in 23 s.
4. Calculate the velocity of a car moving 300 m in 20 s going east towards the mall.
5. Calculate the weight of a 6 kg pizza.
6. A dog runs with a speed of 1.5 m/s on ice. It slides to a stop with an acceleration of -0.50 m/s2. How long does it take for the dog to stop?
7. A ball is hit so that it accelerates at 10 m/s2. The ball hits a glove with a force of 5 N. What is the mass of the ball?
8. A 1.5 x 105 kg train is accelerating. The force applied to the train is 7.0 x 104 N. What is the train’s acceleration?
9. Calculate the momentum of an 8 kg box which slides at 5 m/s.
10. Find the mass of a child who runs at a speed of 4 m/s to get a pizza with extra cheese. His momentum is 120 kgm/s.

some material

Free Fall

Free fall is when gravity is the only force on an object. In the real world falling objects also have air resistance (a type of friction) on them, but this force is so small that it can often be ignored.

g = acceleration due to gravity on Earth = 9.8 m/s2

This value can be used in place of a in our force and acceleration equations. If there was no such thing as air resistance, all falling objects would strike the ground at the exact same time. Even a feather and hammer as astronauts tested on the moon in the video below.

Weight Vs. Mass

In our everyday language these words are often used to mean the same thing, however their real meanings are different. Mass is a measure of the amount of matter in an object and never changes. The SI unit for mass is kg. Weight is the force on a object due to gravity. The SI unit for weight is newtons because it is a force. Weight can be calculated using the following equation:

Weight = m * g

This is just a variation of Newton’s second law using a specific force and a specific acceleration. Weight changes depending on the gravitational force. This is different on each planet due to their differences in mass.

 Click HERE to discover what your weight would be on different planets. Where would you be the heaviest? The lightest?

Apparent Weightlessness

Since there is no where on Earth where we can escape Earth’s gravitational pull, we know that even when we feel weightless, like on a big drop on a roller coaster, we do still have weight. Apparent weightlessness occurs when your body is falling downwards at 9.8 m/s2.

 Click HERE to read some information and do some activities to explain the differences between free fall and apparent weightlessness.

Biology homework help