175

Physics Force & Laws Of Motion Level: High School

The coefficient of kinetic friction between a suitcase and the floor is 0.240 .

(a) if the suitcase has a mass of 55.0 kg , how much works does it take to push the suitcase horizontally with constant speed a distance of 2.70 m across the floor ?

174

Physics Force & Laws Of Motion Level: High School

A child pulls a friend in a little red wagon with constant speed . If the child pulls with a force of 16 N for 14.3 m , and the handle of the wagon is inclined at an angle of 29 degree above the horizontal , how much work does the child do on the wagon ?

173

Physics Force & Laws Of Motion Level: High School

After a tornado , a 0.60 g straw was found embedded 2.9 cm into the trunk of a tree . If the average force exerted on the straw by the tree was 60 N , What was the speed of the straw when it hit the tree ?

172

Physics Force & Laws Of Motion Level: High School

The coefficient of kinetic friction between a suitcase and the floor is 0.240 .

(a) if the suitcase has a mass of 55.0 kg , how much works does it take to push the suitcase horizontally with constant speed a distance of 2.70 m across the floor ?

170

Physics Force & Laws Of Motion Level: High School

A . Assume the block is sliding down the inclined plane and that there is kinetic friction (micro 'k') associated with the block and plane . Label all force vectors . (10 pts)

B . Write a mathematical expression for all force vectors ensure that you use the proper sign . (10 pts)

C . Using the mathematical expression derived in step B derive an expression for the downward acceleration of the block . (10 pts)

169

Physics Force & Laws Of Motion Level: High School

A fire airplane carries a 620 kg bucket at the end of a cable 20.0m long as shown in the drawing that I made . As the helicopter flies to a fire at a constant speed of 40.0 m/s the cable makes an angle of 40.0 degrees with respect to the vertical . The bucket presents a cross-sectional area of 3.80m^2 (squared) in a plane perpendicular to the air moving past it . (The density of the air is 1.20 kg/m^3 (cubed) what is the tension in the cable ? What is the horizontal resistive force on the air on the bucket? What is the drag coefficient assuming that the resistive force is proportional to the square of the buckets speed ?

168

Physics Force & Laws Of Motion Level: High School

A He4 nucleus (atomic weight 4u) moving with speed v breaks up into a neutron (atomic weight 1u) and he3 nucleus (atomic weight 3u). The neutron moves off at right angles to the original he4 (notes this problem works just like a two object system. Keep you mass in u- atomic mass units)

A) If the neutron speed is 3v, determine the final speed and angle of the he3 nucleus .

B) Prove whether of not this "collision" is elastic or inelastic.

167

Physics Force & Laws Of Motion Level: High School

A U-238 nucleus ( mass = 238 units ) decays , transforming into an alpha particle ( mass = 4 units ) and a residual thorium nucleus ( mass = 234 units ) . If the uranium nucleus was at rest , and the alpha particle has a speed of 1.3E7 m/s . Determine the recoil speed of the thorium nucleus .

166

Physics Force & Laws Of Motion Level: High School

High-speed stroboscopic photographs show that the head of a golf club of mass 200 grams is traveling at 52 m/s just before it strikes a 46 gram golf ball at rest on a tee . After the collision , the clubhead travels (in the same direction) at 40 m/s . find the speed of the golf ball just after impact

163

Physics Force & Laws Of Motion Level: High School

A pedestrian walking his dog , waited at traffic lights intersection . Until the walk signal become visible . After stepping out into the intersection he was immediately forced to jump back as a BMW "came out of nowhere" . Although the pedestrian was not hit , his dog was . On hitting the dog the driver slammed on his brakes and skidded to a halt . The BMW driver claimed the driver of the BMW must have run a red light as the walk signal was illuminated . The driver of the BMW claimed the light was green and the pedestrian stepped onto the intersection without looking .

WHO IS TELLING THE TRUTH ?

1. Length of the skid mark left by BMW after it hit the dog, 78.6m .

2. Road surface was dry asphalt . Co-efficient of friction between tyres and asphalt surface is 0.6 . All the Kinetic Energy of the BMW is dissipated by friction with the road surface during the skid .

3. The BMW was in a 80Km/h zone .

4. The distance between the intersections is 482m .

5. The traffic lights are timed so that there is 19.5's between first set of lights turning green and second set of lights turning green .

6. Mass of BMW is 5354 kg .

7. Standing starts times for BMW

0-60 km/h 4.8 seconds

0-80 km/h 7.0 s

0-100 km/h 9.6 s

0-120 km/h 12.9 s

0-160 km/h 22.5 s

400m 17 s

Rolling start for BMW

40-70 km/h 2.7 s

60-90 km/h 3.4

s 80-110 km/h 4.0 s

162

Physics Force & Laws Of Motion Level: High School

An elevator can hold 20 people with an average of 75-kg mass . The elevator itself has a mass of 500-kg . The cable supporting the elevator can tolerate a maximum force of 2.96 x 10^4 N . What is the greatest acceleration the elevator motor can supply without breaking the cable ?

161

Physics Force & Laws Of Motion Level: High School

A student stand on a bathroom scale in an elavatorat rest on the 64th floor of a building. The scale reads 836 N . (a) As the elevator moves up, the scale reading increases in 935 N , then decreases back to 836 N . Find the acceleration of the elevator. (b) What is the bathroom scale really measuring ?

160

Physics Force & Laws Of Motion Level: High School

A cyclist just for kicks decides to roll down a 400 meter hill starting from rest and not pedaling or using his brakes . The cyclist and bike together weigh 180 lbs . if the coefficient of friction is 0.13 and the hill is inclined at an angle of 8 degrees find the cyclist's speed at the bottom of the hill .

159

Physics Force & Laws Of Motion Level: High School

A car pulls a trailer weighing 700 lbs along a level road . If the car pulls with a force of 2000 N the trailer attains a speed of 20 mph after moving 30 meters starting from rest . Find the coefficient of friction between the trailer and the road .

158

Physics Force & Laws Of Motion Level: High School

A rocket engine has the following thrust curve in pounds:

Time / Thrust: 0.13 second 99.061 pounds

Time / Thrust: 0.38 112.202

Time / Thrust: 0.63 118.164

Time / Thrust: 0.88 121.774

Time / Thrust: 1.14 123.731

Time / Thrust: 1.39 119.989

Time / Thrust: 1.64 115.161

Time / Thrust: 1.90 106.825

Time / Thrust: 2.15 94.019

Time / Thrust: 2.41 82.262

Time / Thrust: 2.66 48.434

Time / Thrust: 2.91 13.668

Time / Thrust: 3.17 3.033

Time / Thrust: 3.42 0.000

Burn time…..: 3.420 seconds

Tavg Lbs (Average Thrust inPounds)…..: 97.5776

Tavg Newtons. (Average thrust in Newtons): 434.047

Totlmp Lbsecs: (Total Impulse in PoundSeconds) 292.326

Totlmp Ntsecs:(Total Impulse in NewtonSeconds) 1300.330

The rocket engine is attached to the rear of a small bicycle. The weight of the bike and the motor is 35 lbs. The rider weighs 155 lbs. The bike has good bearings and tires, and rolls easily. The rider is bent down low to reduce the drag of air resistance. The track is straight and flat.

The bike is pushed up to a speed of 5 mph . Then the motor is ignited . What will be to top speed of the bike in mph and how far will it have travelled at motor burn out ?

Calcuation is same as the above problem except 'u' is not equal to zero but is equal to 5 mph .

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