Locomotive joint （估计是种病）

1.Locomotive exert on a 12320-kg boxcar to make it accelerate forward at 0.57 m/s2.How long will it take the boxcar to reach its cruising speed of 82 km/h (51.0 mph or 22.8 m/s)?
已知：V0=0,m=12320kg,a=0.57m/s²,Vt=22.8m/s.
求：s=?
由Vt²-V0²=2as有,s=(Vt²-V0²)/2a=(22.8²-0)/(2×0.57)=456m.
答：略.
2.The builders of the pyramids used a long ramp to lift 22000-kg (22-ton) blocks.How much work was done in raising one of the blocks to a height of 53
已知：m=22000kg,h=53m,g=9.8m/s²
求W=?
由公式W=mgh有,W=22000 × 0.8 × 53=11426800J
答：略.
3.If your car accelerates from rest at a steady rate of 4 m/s2,how soon will it reach 88 km/h (54.7 mph or 24.4 m/s)?
已知V0=0,a=4m/s²,Vt=22.4m/s
求：t=?
由公式Vt=V0+at有,t=(Vt-V0)/a=(22.4-0)/4=5.6s.
答：略.
4.On Mars,the acceleration due to gravity is 3.71 m/s2.How far would a rock fall in 5 s if you dropped it on Mars?
已知g'=3.71m/s²,t=5s
求：h=?
由公式h=gt²/2有,h=3.71 × 5²/2=46.25m.
答：略.
5.A basketball player can leap upward 0.44 m.What is his initial velocity at the start of the leap?
已知：h=0.44m,g=9.8m/s²
求：V0=?
由公式h=V0²/2g有,V0=√(2gh)==√(2×9.8×0.44) ≈2.94m/s
答：略.
6.A sprinter can reach a speed of 9.4 m/s in 0.95 s.If the sprinter’s acceleration is constant during that time,what is the sprinter’s acceleration?
已知：V0=0,Vt=9.4m/s,t=0.95s
求：a=?
由公式Vt=V0+at有,a=(Vt-V0)/t=(9.4-0)/0.95≈9.89m/s²
答:略.
7.How much does a 84-kg person weigh on earth?
已知：m=84kg,g=9.8m/s²
求：G=?
由公式G=mg有,G=mg=84×9.8=823.2N
答：略.
8.As water descends from the top of a tall hydroelectric dam,its gravitational potential energy is converted to electric energy.How much gravitational potential energy is released when 900 kg of water descends 230 m to the generators?
已知：m=900kg,Δh=230m,g=9.8m/s²
求E=?
由公式ΔEp=mgΔh有,ΔEp=mgΔh=900 × 9.8 × 230=2028600J
根据能量守恒定律：E= ΔEp=2028600J
答：略.
9.You’re using a wedge to split a log.You are hitting the wedge with a large hammer to drive it into the log.It takes a force of 3100 N to push the wedge into the wood.If the wedge moves 0.2 m into the log,how much work have you done on the wedge?
已知：F=3100N,S=0.2m
求：W=?
由公式W=FS有,W=FS=3100 × 0 .2=620J
答：略.
10.You’re sanding a table.You must exert a force of 32 N on the sandpaper to keep it moving steadily across the table’s surface.You slide the paper back and forth for 21 minutes,during which time you move it 1000 m.How much work have you done?
已知：F=32N,t=21min=21× 60s=1260s,s=1000m,
求W=?
由公式W=FS有,W=FS=32× 1000=32000J
答：略.

would 后面应该接动词原形,would do 表示的是一种过去的习惯.而would have done 是一个虚拟语气,用在句型：If i had done something, I would have done something 中.

他们希望史蒂芬森建个火车头来,用来把装了煤矿的车从矿洞里拉出来