# 10 Physics questions: Acceleration, speed, air resistance, density, temperature, work

1. You push with a 50-N horizontal force on a 10 kg mass resting on a horizontal surface against a horizontal friction force of 20N. What is the acceleration?

2. A railroad diesel engine weighs six times as much as a freight car. If the diesel engine coasts a 7km per hour into a freight car that is intially at rest, how fast do the tow coast after they couple together?

3. A car moving at 20km.h skids 10m with locked brakes. How far will the car skid with locked brakes at 120km/h?

4. A cannonball shot with an intial velocity of 150m/s at an angle of 45 degrees follows a parabolic path and hits a balloon at the top of its trajectory. Ignoring air resistance, how fast is the cannonball going when it hits the balloon?

5. A vacationer floats lazily in the ocean with 93% of his body below the surface. The density of ocean water is 1,025 kg/m^3. What is the vacationer's average density?

6. What will be the final temperature of 100g of 25 degree C water when 100 g of 45 degree C iron nails are submerge in it. (The specific heat of iron is 0.12 cal/g. The specific heat of water is 1.00 cal/g.)

7. An electric iron connected to a 100-V source draws 10A of current. How much heat (in joules) does it generate in a minute?

8. A weight suspended from a spring is seen to bob up and down over a distance of 40 centimeters twice each second. What is frequency? Its period? Its amplitude? Include units.

9. Balance the chemical equation and be sure to show your work!

___ CH4 + ____O2 → ____CO2 + _____H2O

10. How many grams of ozone, O3 (48 amu), can be produced from 96 grams of oxygen, O2(32amu), in the following reaction - show all work!

3 O2 → 2 O3

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#### Solution Preview

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1. You push with a 50-N horizontal force on a 10 kg mass resting on a horizontal surface against a horizontal friction force of 20N. What is the acceleration?

In order to find the acceleration, first we need to calculate the net force on the object.

F1= 50N F2= -20N

FT= F1+F2

FT= 50-20

FT= 30 N (1N= 1kg.m/s2)

Now we can calculate the object's acceleration "a" by dividing the net force to its mass.

m= 10 kg

a= FT/ m

= 30 / 10

a = 3 m/s2

2. A railroad diesel engine weighs six times as much as a freight car. If the diesel engine coasts a 7km per hour into a freight car that is intially at rest, how fast do the tow coast after they couple together?

We don't know the masses of diesel engine and the freight car. However we can show them with variables in terms of each other.

Mass of railroad diesel engine m1= 6m

Mass of freight= m2= m

mT = total mass when they couple = m+6m= 7m

V1= Initial speed of diesel engine = 7km/h

V2= Initial speed of freight car = 0 (at rest)

VT = final speed

We are going to use the momentum formula:

m1*V1 + m2*V2 = mT*VT

6m * 7 + m*0 = 7m* VT

VT *7m = 42m

VT= 42m/7m

VT= 6 km/h is the final speed of the total mass.

3. A car moving at 20km.h skids 10m with locked brakes. How far will the car skid with locked ...

#### Solution Summary

With excellent explanation and calculations, the problems are solved.